I'm a lifeguard, but work half the time as a recreation assistant, which is probably the same as what your going for. You need to be confident/have good communication skills, teamwork, the usual stuff really. First Aid qualifications would probably help a lot, or just a willingness to learn. And you need to be fairly independent and do things that you can see need doing instead of waiting to be told. Competition depends on where it is really, but I can't imagine there being a huge amount - where i work theyre always looking for new staff, and it's the same at other leisure centres near me. Good luck anyway!