Ok, to all of our loyal followers who swim, I need some advice. I am finally to the point where there's no longer any real threat of drowning, so I can concentrate on swimming a little more. The other day, I was asking the lifeguard for some advice on breathing and stuff, and one of the comments he made while watching me swim was that I use my legs a lot. I didn't think I was, but I wasn't really thinking about it much, as I was more focused on breathing air instead of water, etc.
Today, I felt comfortable enough that I could think about something other than breathing, and I realized that I was indeed using my legs a lot. I tried to use them less, and found that I got tired really quickly. My upper body is apparently weak. So, assuming I try to incorporate some gym time into my workout routine (which right now consists of swimming and watching Netflix movies from the couch), what should I concentrate on trying to strengthen to help improve swimming?