I don't use the pen but use the lancet freehand. I find that the clicking noise of the pen startles the cat and I also have better control freehand
When you look at the ear you should be able to see the vein running around the edge of it. You want to aim for between the vein and outer edge of the ear. Also use a paper towel or cottonball to support the ear. Either massage the ear before and after you poke to get the blood to flow or you can warm it using a warm washcloth or rice sock.
Don't worry if you do not get blood on your first time. Sometimes it takes some time for the ears to learn to bleed. That is why the massaging helps. Massage towards the area you poked.
Also, if you do get the vein, don't worry it won't hurt your cat. It just bleeds a lot more blood then you will need. You can hold your finger or a tissue over it for a moment until it stops bleeding. If you don't and your cat shakes his head, your walls may look like a scene from CSI. :lol:
Good luck with your first test and welcome to the Vampire Club. :mrgreen: