crwdns2893792:0crwdne2893792:0 Josh White ,
The best training is simply doing it. Use youtube and ifixit, they have all the training you will need. For serious apple issues, gsm-forum is very helpful. For android issues, xda-developers. Nothing teaches you like experience. Buy a few cheap, broken phones of your own off of ebay and give them a go. Phone repair is not very hard, at least things like changing screens and cables aren't difficult. Just be confident, and watch lots of videos!