Most Helpful Girl
Don't, especially if she is in the middle of working out. If you really feel the need to say something tro to catch her when she is taking a break... not in the middle of what she is doing. There is a time and place for everything but I can tell you that when I am working out the last thing I want to do is socialize with anyone.
Most Helpful Guys
Mostly you don't
Unless you are in a fitness class, and you have to partner up with her, you can talk.
If you are at wieghts hall, you can try to share a machine with her if you are really interested in her, but that might not get you more than hi.
And you will have to actually take the weights off and on and she will watch you lol and never thank you.
You don't, probably; the hot ones expect you to and as such they aren't going to be interested. You can give them a few looks but I wouldn't bother with a direct approach.