Pin goes all the way in, pull back the plunger a bit to see if blood gets drawn into syringe. If none, complete pinning with your AAS cocktail. Yep, I do every time. It takes about two seconds of your time.
Doesn't mean I never get blood upon removing the syringe. If you've nicked a vein on the way in, you'll get some blood. Nothing to worry about, however.