Resign yourself to the fact that you will be very frustrated at times and you will be wasting canned food as they turn up their nose at it. Also, you may want to immediately switch your cat to a dry food that has fewer calories from carbohydrates than most dry foods. (e.g., EVO)
Keep in mind that different tricks work on different cats:
If your cat has been eating dry food on a free-choice basis, take up the food and establish a schedule of 2 - 3 times per day feedings. I really do prefer just twice-daily feedings when trying to transition them. A normal, healthy hunger response after 12 hours goes a long way to convince them to try something new.
Once the cat has transitioned to canned food, I prefer to either free-feed them (if they are not too fat) or to put out a meal 3-4 times per day. Small cats in the wild eat 8-10 small meals per day. I do not worry about leaving canned food out for up to 12 hours at a time. Keep in mind that a lion is not going to eat his entire prey immediately.
If you want to take the transition very slowly, you can feed the amount that your cat normally consumes in a 24 hour period - split up into two feedings to get him used to meal feeding. Many people, however, are unsure as to how much their free-fed cat really eats so I would start off by figuring out the calories that your cat needs to maintain his weight if he does not need to lose any weight.
Again, most cats only need 150-250 calories/day. The dry food bag should tell you how many calories are in a cup of food but if it does not, you can call the company.
Leave the dry food down for 20 minutes, and then remove any uneaten portion. Repeat in 8-12 hours depending on if you are feeding 2 or 3 times per day. During the first few days of transitioning to a set schedule, you can offer canned food during the dry food meals, or in-between meals. The stubborn ones, however, will not touch it. Do not despair - all cats will eventually eat canned food if their caregiver is determined, methodical, and patient enough. Once your cat is on a schedule you will notice that he is more enthusiastic about food during his proper mealtimes and will be much more inclined to try something new.
Once you have established scheduled mealtimes, you will most likely need to start feeding a bit less at each mealtime in order to get the normal sensation of hunger to work in your favor. Again, we are trying to use the normal sensation of hunger to help us out. We are not trying to starve the cat into the diet change.
Once your cat is on a schedule of meal-feeding instead of free-feeding, try feeding a meal of canned food only. If he will not eat it - and the very stubborn ones won't - try not to get frustrated - and do not put down dry food. Try some of the other tips listed below. If he still will not eat the canned food, let him get a bit hungrier. Offer the canned again in a couple of hours - or just leave it out. Some cats will be more apt to try something new if they keep walking by it and seeing/smelling it. Try a different brand/flavor or a different 'trick'. Once it has been ~18 hours since he has eaten anything, give him just a small amount (1/4 of a cup - or less if it is EVO) of his dry food - keeping track of his daily caloric intake.
Remember to be patient.
Exercising your cat with a tassel toy before feeding can also help stimulate his appetite.
Cats' noses are much more sensitive than ours are. They can smell the dry food in the cupboards. I suggest either putting it in the refrigerator or putting it in a tightly sealed container. If they can smell it, they will hold out for it. Some people recommend getting it out of your house completely, but this is not possible when you are dealing with a very stubborn cat that needs a bit of time and patience to make the transition happen.
The following worked for my cats: Sprinkle a very small amount of tuna – or any other favorite treat (some cats do not like fish and would prefer cooked chicken) - on top of the canned food and then once they are eating this, start pressing it into the top of the new food. (The “light” tuna is better than the fancy white tuna because it has a stronger smell. Or, Trader Joe’s makes a Cat Tuna that is very stinky.) Be careful to decrease the amount of fish as soon as possible. Health problems can occur with a predominantly fish-based diet. Plus, you do not want to create a situation where your cat will only eat very fishy foods.
Make sure that any refrigerated canned food is warmed up a bit. Cats prefer their food at 'mouse body temperature'.
Try offering some cooked (or raw - whole meats, rinsed well or partially baked) chicken or meat baby food. One of the goals is to get your cat used to eating food that does not crunch. He needs to get used to a different texture. Also, chicken is a great source of protein to point him in the proper direction toward a high protein, low carbohydrate diet. If he eats the chicken, he may head right into eating canned food. Then again....he may not.
Try sprinkling some parmesan cheese on the canned food. Most cats love parmesan cheese and this trick has been very successful for me.
Try a product called FortiFlora - feline version. Most cats LOVE FortiFlora and this has recently become my favorite trick. This is a probiotic made by Purina but you are not going to use it for its probiotic properties. You are just going to use it as a flavor enhancer. The base ingredient in FortiFlora is animal digest - the very substance that makes dry food so very enticing to cats. The directions say to use 1 package/day - and you can use this much if you want to - but this amount is not usually necessary. You may only need ~1/4 of a package - or much less - with part mixed into the food and part sprinkled on top of the food just as you would use salt and pepper on your own food.
FortiFlora can be purchased online but an easier product to find is Temptations treats. I trap a lot of feral cats for spaying/neutering purposes and this is one of the best baits that I can use. These tasty treats can be found at most pet stores. Put a few in a baggie and crush them with a hammer. Use the crushed treats as described for the FortiFlora above.
There are numerous freeze dried meat treats on the market that you can also sprinkle on top of the canned food. Halo's Liv A Littles is a popular choice.
Speaking of texture, a common question is "can I just soak the dry food in water?" I hedge more than just a bit at this question. Dry food often has a very high bacterial content. Mold is also often found in dry food. Both organisms flourish in moist environments. There have been many deaths of dogs and cats secondary to eating mold mycotoxins, vomitoxins and aflatoxins which often contaminate the grains found in dry food. If you want to try the trick of wetting down the dry food to alter the texture, please leave it out for only 20-30 minutes then discard it.
Try dipping some dry food pieces in the juice from the canned food. Some cats may refuse to eat it if the dry food even touches the canned food. But if he will eat it with a bit of canned juice on it, try the 'chip and dip' trick. Scoop up a tiny bit of canned food onto the piece of dry food. Put them on a separate plate from his small portion of dry food. Some cats will eat their small portion of dry and then go investigate the dry food with a tiny bit of canned on it.
Going one step further, try adding a few small pieces of the canned food to the small portion of dry food. Your cat may pick around the canned food but will get used to the smell - and texture - even if he does not eat any pieces of the new food.
Crush some dry food and sprinkle it on the top of the canned food.
If you do not think it will upset your cat, try gently rubbing a bit of canned food or juice on the cat's gums This may get him interested in the taste and texture of the new food - but do it gently. You do not want to make this a stressful situation and create a food aversion. (This trick is commonly used to get just-weaned kittens used to eating canned food.)
If you do not think it will upset your cat, use your finger to put a tiny bit of canned food or juice on his paw for him to lick off. This has not worked for me in the two cats I have tried it on but it is another idea. Make sure you do it without stressing your cat. Again, you do not want to create a food aversion.
If you have a multiple cat household, some cats like to eat alone in a less stressful environment, so you may need to take these cats into a separate, quiet room to think about the error of their ways - their carbohydrate/dry food addiction. Once in a quiet setting, away from the other cats, two of my cats would eat canned food/tuna ‘meatballs’ by hand. Not from a bowl, mind you, but only from my hand. I’m not sure who was being trained. They did eventually start eating from a bowl after a few hand feedings.
Try various brands and flavors of canned foods. Try Friskies, 9-Lives, Fancy Feast, etc. Many cats prefer the foods that are all by-products and turn their noses up when offered the by-product-free diets like Wellness, etc. You can worry about feeding a a different canned food later if you want to and you can always mix different types of food together. The initial goal is just to get your cat used to eating canned food and not dry kibble. And remember what I said above. I would much rather see a cat eating a canned food like Friskies, 9-Lives, or Fancy Feast rather than any dry food.
Syringe-feeding is also another option but has to be done with finesse and patience so as to avoid a food aversion. If you choose to syringe-feed, your goal is not to feed him a full meal. Sometimes just syringing a 1-2 cc's can 'jump-start' your cat into eating the canned food - maybe not the first time but it will at least get him to taste the new food and experience a foreign texture. The best way to syringe-feed is to kneel on the floor with your cat between your legs so he is facing the same way as you are. Then, using a small (1cc/TB) syringe, slip it in the side of his mouth and give about 1/2 cc at a time. He may spit it out but you are just trying to get him used to the taste and texture, not stress him.
Few canned foods will make it through the tip of a syringe but human meat baby food works well for this trick. You can also water it down a bit if you need to.
If you want to use canned cat food instead of baby food, you will need to cut the end off of the syringe so that the opening is as big as the barrel. Make sure that the tip is smooth. If you do not want to cut the tip of the syringe off, you will need to puree a pate (versus chunks) type of food. I puree Wellness for this. I run it through the blender with a small amount of water (~3-4 tablespoons/5.5 ounce can). Then I strain it to remove anything big enough to clog the small tip of the syringe. Wellness is also a balanced diet - unlike human baby food.
Even though human baby food is not a balanced diet for long-term use, it is a great tool that can be used to help transition a cat to a texture that he is not used to.
I did have to take drastic measures for a foster cat named Molly. She was dangerously obese (20 lbs - double what she should have weighed) and would not eat canned food even after two weeks of syringe-feeding her. She needed to go in for a dental so while she was under general anesthesia, I put in a feeding tube. This took the stress off of both of us. After two weeks of feeding her via the tube she started licking the canned food from my fingers then suddenly decided it was time to eat it. She then started to finally lose weight. Before the 7 lbs weight loss, she could barely walk, could not clean herself, and was quite possibly headed for diabetes.
Don't give up. One of my barn cats ate dry food for the first 12 years of her life. She would never touch the canned food that the other cats ate. Then, one day, she found her 'inner carnivore' and started eating canned food out of the blue! I was shocked. That was 4 years ago and she has been on a 100% canned food diet since she made the switch.
These are just a few tricks that you can try. Different tricks work on different cats. The key is to be patient. Remember, it took me three months to get my cats on 100% canned food. Most cats, however, will not take this long.