Like brehs said already, either catch ‘em leaving or coming into the gym. I don’t approach while they’re actively involved in a workout or have headphones in.
If I do approach I usually ask their name and how long they’ve been working out, what got them into working out. Usually that opens the conversation cause they LOVE talking about their journey. But I NEVER get contact info on first meeting. I wait until I see em once or twice after the initial interaction to close

Just gotta find what works for you. But again, I’m of the don’t shoot shots in the gym cause women talk and I’ve seen shyt go south FAST. I’d rather approach in places that I don’t consider “home turf” for lack of a better term.
And no. Never at work