> there’s a number of people [at the gym] who want to be left alone and can be irritated if you interrupted their workout to talk.

This one is pretty easy. Look for the people who spend more time yapping than working out. They generally love to meet new people. The opposite case is pretty obvious too. Don't approach someone just as they are preparing to start a set or if they're going hard on a treadmill or bike. Generally, if someone is not talking to anyone and seems locked in, earbuds in, etc. probably leave them alone. But asking for a spot when they're between sets is an easy excuse to at least get their name. Nobody is going to really mind that, and you'll pick up pretty quickly whether they're talkative or not.