www.hip2save.com and
www.pennypinchinmom.com are my personal favorites. I have a personal facebook couponing page called Spring Hill Coupon Queen. It posts a lot of area specific deals for me, but has some national freebies and matchups, too.
As for tips, don't overwhelm yourself right off the bat, don't feel like you have to have a MASSIVE stockpile in order to be saving tons of money, and most of all, enjoy it. For me, it's like a game, or a challenge. Couponing is a rush for me- total, pure, unadulterated thrill. When it becomes a chore, it's no longer fun, and you'll just give up.