How to be a great swimmer?

Okay so it is almost summer, and I can't wait until I go to Wildwood! (New Jersey). There is a ride that has a pool that is 10 ft. deep. And is only for good swimmers. I can swim, but I am not great, I am slow at swimming to so everyone will be waiting for me to leave the pool.I am not an adult but not a kid, so yeah. I want to learn to swim better, not super sonic fast, just at a good rate. Last year, I went on the ride and I was fine, but I felt like I was going to drown. No, I am not chubby, I am fit and have a average weight for my age, sometimes underweight because of an illness. I don't know why but swimming takes a lot of energy away, I use so much energy then I get a few inches. Wow. But I want to be able to swim better. So life will just be easier. I am 5.2 or something like that so if that helps. Technics or ways to help will be Fine, I am not looking to be Michel Phelps I just want to be quick and have it a breeze, thanks