If you are gonna do it, think about it like a medical procedure, dont re use a needle even the same day cause they get dull, your veins will become damaged if you do it multiple times a day so Ideally you rotate between all 4 veins in the crook of your arm. Dont rush, make sure you are in the vein with a register if you have to much trouble and it starts hurting just fucking snort or smoke the shit because when you get desperate thats when youll just pull the plunger regardless of being in the vein