This could turn into a very good source of information...for newbies and old pros alike.
List some of the little things you have learned since you started using gear...not the stuff normally seen on these boards, just little intricacies.
1) Order your syringes with the drawing pin already on them (20-21g)...this cuts down on handling the syringe and the needles.
2) I can't inject delts or traps the day after working bis...they cramp...I end up rubbing my arm to remove the cramp...while a syringe is left dangling from my flesh (this results in pain later on).
3) Prior to injecting, stretch the muscle you are injecting...don't flex it.
You get the point...let's hear some of your advice