I think you need to mix it up a bit and don't just swim freestyle ad nauseum.
Watch YouTube instruction videos, use a pull bhouy so you can focus on your arms and vice versa with a float.
Try and look at a few different routines on the Web swimming different sets at different paces.
I don't...
I swim three times a week, wouldn't classify myself as that serious though, freestyle 1,000 m in about 19 minutes. I want to start doing more open water swimming outside of the summer months so need to invest in a wet suit!
Self taught myself about 4 years ago.