Heres what you do to combine everyones advice and my own.
1 - get lucky and play well in otp with gm's, captains, and well known players.
2 - wait for mid season camps / topics asking for FA's. there will be players on current teams that will be dropped at some point in the season most likely.
3 - be sure to check the site on game days early in the day and early in the evening. if a team doesnt have enough players they will ask for an ecu, which can only be a registered player who is a FA. Golden oppurtunity above them all.
4 - just in general dont bug the hell out of everyone and play good/be willing to learn and get better. if your not on a team, you may need to work on your game a bit, theres only 8 teams and another season will come in the future eventually with hopefully twice as many teams but only time will tell
good luck! rub your duck!