Technique question?

To inject syringe to get instant blood back when hitting the vein u need to put the plunger back all the way before entering the skin or right when u make injection,? Is it supposed to be normal that once your under the skin and u pull the plunger it returns to the same possition instantly? Or do u need to hold the plunger and inject until u see flashback it should happen by itself? And then don't move and inject the rest?