After creating a player and signing an agent, go to the draft and start the draft. You will probably be selected in the third round unless you imported your player from NCAA Football 06 or NFL Street 2. If you do not like the team you got drafted by, then simulate the preseason. When the preseason is over go to your agent's office on the city map. Scroll down to "I demand a trade" and you will be traded to another team. If you dislike that team as well, then demand another trade. Be careful, as you can only demand two trades until the next season.