Football is the most played, and hardest to me as a casual player. I make a lil on basketball and baseball, but I don't really invest much time/money into it. I would say start out in the 50/50 and double up contests, and don't do the huge multi-entry contest with small chances to cash.
There are a few accounts on Twitter where you can find lineups posted 3-4 hours before the games and go from there. Free info is everywhere as far as daily matchups and trends, so I usually glance around, then form my own opinion and make my picks. I would recommend reserving entry's with a lineup early in the day, then adjusting after lineups come out, or late changes before lock.