Besides practice you should reference on what you are painting. For example I just painting the Houston Oilers and old school New England Patriots. Which i'll post a picture of in the other forum. They were pretty straight forward simple wise, however I would suggest doing your predominant colors first and then touch up afterwards. In this case the Patriots pants needed to be painted red and their shirts were white and the helmets are white. Well the figures I had were from miggle and unpainted in white, so my white was solved. All I had to do is the red and then the fine stuff such as stripes and logo on helmet. I always do the flesh colors last then touch up any mistakes. Once I'm done I spray the players with Testors dullcoat and then put a glosscoat on the helmets. Just remember you are your worst critic so if you are perfectionist you'll do great. Just enjoy it and have fun.
To reference you might want to look at this site. I found it to be helpful and has football uniforms past and present
http://www.weirdwolf.net/FFP/index.htm
Thanks
Mike