I have always used the lancet device because it's consistent.
I realize that many just poke freehand but seriously, how consistent can you be freehand? You can't.
Be sure you have a lancet device on which you can dial a depth setting.
Dial to the most shallow, put your finger behnd the ear tip, rest the device against the ear, and release the lancet with the button.
if you get a drop of blood; great. if not, adjust to 1 setting deeper and try again.
Cats do like consistency, no surprises, so knowing exactly how the poke will feel, every single time, is very important. If the cat never knows if it will hurt this time or not, you may not have a cat who is fine with testing.
you can try freehand, but I believe the device is more friendly
Gayle