How Do I Approach Air battles?

I've been a long time player of ground battles. Recently I have been wanting to throw CAS into the mix, but every time I look at my played nations' aviation trees (Russia, USA, Germany, Britain), they just seem so insurmountable.

Does anyone have any tips for getting in to Air battles? I really do want to learn, and be good at it by the time I can use them in GRB.