As usual Red covered almost everything
The only things I have to add are learn LOTS of training techniques as different dogs learn different ways. There are SO many trainers that are either one way or another, like they're all about clicker training, and they think that prongs are the worst invention on the planet. Go to every seminar you can, talk to every trainer you can. Lots of training places let you watch classes, pick up tips see how the trainers act with the different dogs. Learn breed traits, but keep in mind, that a dog doesn't always act the way they're supposed to. Also, like Red said, be VERY careful with strange dogs. People don't know everything about their dogs, something they do subconsiously can freak their dog out, or they don't know that their kid hits the dogs with blocks when they aren't looking, or they got the dog from someone else, and the someone else let the dog wallow in bad habits, or even abused them.
The internet is a great tool but nothing compared to first hand knowledge and experience. As in everything in the dog world, find a mentor. They can help you so much and let you know what you can and can't handle. And if you trust your mentor, LISTEN to them.
Good luck.