I don't know. That's the problem: all the stuff I watch and read is so vague and even contradictory ("push yourself, but don't push yourself too much!"), and so one-size-fits-all that I have no idea where to even begin at this point. It's like learning some skill that takes years, except if you get it wrong you ruin your body and are left in pain.

In general, you can't teach yourself how to lift safely. You want to start with a trainer.