Do lots of research before choosing a company- check out our review section to read about other traveler's opinion of different companies. If you want to get most of your paperwork out of the way now, I would fill out applications with a few different companies. Once they have your application materials on file, they can submit you to different assignments whenever you are ready. You will have to apply for licensure in the state you'll be traveling to, though, and I would wait to do that until you actually have an assignment lined up.
Things you should expect from travel companies- free first-day medical & dental insurance, 401k, travel & liensure reimbursement, free private housing, no less than $30/hr (more depending on where you travel to). There are enough travel companies that offer these things, that you should not settle for less.