One of the easiest ways is to just push the plunger into the syringe HARD before putting it into the insulin and then just "let go"
There's a little vacuum that will suck a tiny bit up into the needle.
Or you can experiment with your syringes and learn to count drops. Pull up a "known amount"....then slowly twist the plunger to produce the same size drops and count how many you get. (example....in .25 unit, you can get 3 same-sized drops)….so if you want 1 drop, you'd pull up .25 and waste 2 drops