I shouldn’t have to say this, but— do not sign anything which has important points added in goddamn pencil.
Don’t sign forms with areas left blank. Make sure those areas have “not applicable” written in each one (or words which work where you are).
Be aware of ambush tactics like being asked to sign unrelated forms * after * a surgery, any painful therapy, while feverish — any time when you’re unable to read and think clearly.
Don’t believe “this form is no big deal, you don’t have to read it.”
If you’re pressured “because it’s more efficient to sign everything at once” or anything like that, remember this is one more reason to be cautious, if not suspicious. Tell them to make a separate appointment.
If you are in pain, alone, or concerned for yourself and your ability to refuse to sign papers under pressure, ask someone to be there with you.
If you don’t have people to help in person, get someone to witness things with your phone, and allow them to say “wait a minute, that’s not right” or “no” for you. You don’t even need a smart phone to do this, OK? I’ve had to use a land line on speaker. It helps if your person has a clue what’s going on, but if you’re ambushed, just make sure they are willing to stick up for you. There are probably notes on how to be an advocate somewhere, if you know resources please add them in comments or add to this post.