How much should I aspirate?

So when I aspirate how much should I pull back? Because the first time I injected it hurt for a couple days, but when I aspirated no blood came in and I injected. The second time I injected, on the other glute I aspirated, no blood and injected but unlike my first injection there was no minor pip.

You only need to pull back slightly and if you are in a vein, blood will get in syringe quickly.

Generally speaking it is good to use recommended injection sites to limit the chance of coming in contact with any significant underlying vasculature or nerve