[Tom Bayes]

I will mostly repeat others advice:

If there are multiple limpers and you are not heads-up, then I will draw 4 to an A or K and five otherwise. In this situation, I don't think there's much point in trying to hide your weakness. You are just hoping to catch a big hand on your 2nd try. I've won tons of hands catching 2 pair or trips or even pat hands after discarding 5.

It's a harder and more interesting decision heads-up. The decision then is often dependent on what the opponent limps with. If this person limps with short pairs or will complete in the small blind with any pair or stuff like AK/AQ, then I'll draw 3 to any 2 cards ten or more-often pairing paint will be good enough in this situation. If the player routinely limps with draws, then you can often win with your unimproved high cards if they miss (especially if it's a goober that draws at low straights).

If the opponent will muck low pairs and only limps in with high pairs, then I'd draw 4 or 5 if the person is difficult/impossible to bluff, but 3 if the player is a weak-tightie that would muck any pair if they fail to improve.