This topic has been discussed alot, but I think you will notice on various threads that few people have actually picked up at the gym.
Here's my 2 cents.
First, befriend the people working there. All of them, even the pompous alpha male wannabe guys. You never know who would unwittingly ****-block you otherwise. It happened to me before at a gym
Second, if your gym has an organized sports league with games like volleyball. Do that. This is your easiest chance to socialize. My gym also has tennis. When I have more time, I'll definitely do that because I've met girls at tennis before.
On the girls that work at the gym. I found this because I want to know what to do there. One time I had all the signs of interest from a girl that worked there, but kind of chickened out on asking her out. It was partially due to the fact that I have a gf and had at the time, but mainly because I didn't want to deal with the awkwardness if it didn't work out.
What do you know a year later, another girl seems to be into me. You can tell the difference from them just being friendly. If a girl that works there goes out of her way to talk to you, it's pretty likely there is some interest. Consider it the same for any other girl there
What I've found for years are there are a few types of girls at a gym
1) The type that is so self conscious and is just there to lose a few pounds and would rather not talk
2) The type with boyfriend or husband that doesn't really want the attention
3) The attention ***** (note her with the belly baring and spandex outfits). This is the girl that wants the attention of all but may put up her ***** shield
4) The decent girl who does like to workout but isn't opposed to meeting someone there
5) The girl that works there. If they are single they will be looking to hookup, doesn't matter if it's a guy that works there (more likely) or a guy she likes in the gym.
Remember since you can see them time and time again, you can move slower. However don't move too slow. You've probably noticed turnover can be high at some of these gyms. I know I waited too long on my redhead Pilates/Yoga hottie girl.
Oh by the way they say to try Yoga (that girl used to teach it), but I've never had the balls to do it yet. I'm not flexible enough either!