play small at first. You'll pickup things as you play. As you become more comfortable with figuring the odds versus the game situation, don't be afraid to lay long odds. I find that much of my profit comes from laying 1100 to win 100, in a situation where I will lose (I estimate) 1 in 20 or less often. And you will lose some of those. Most people don't have the stomach or bankroll to do that, and would much rather have the +1100 side, so they can bet small. Take advantage of the +EV opportunity.
Another tip -- well, a mistake that, amazingly, I still make is this: you need to remember that during live betting, if you're making offers (you should), girlfriends, wives, kids, phones, taking a piss, eating, and changing channels during a commercial ARE YOUR WORST ENEMY!! Don't hang that line up there without having both eyes on the game! Don't get distracted! It's very easy, and I've lost untold amounts of money by doing so, and still occasionally goof this up. When Brady fumbles after being sacked and the Jacksonville recovers, and you're mid-stream taking piss, it's WAY TOO LATE to take down that New England -224 that your were offering. The order is filled, and the new odds are now Jacksonville -120/New England +102. You've got New England at -224 for 3 dimes. Ouch!
One more - watch out for the trap setters. You'll see people offering something WAY out of whack, like Alabama at -700, towards the end of tonight's game, where the proper odds, and best available offer, is +300. People do that because every once in a while, this happens: you click the box for the best odds (in this example, Ala +300), and quickly enter your bet and click confirm to lock in the price. You're grabbing some 'bama at +300 for whatever reason (hedging, value, fun, etc.). Just before you clicked the +300 box, however, that offer was taken down, or filled. As that happened, the crazy Alabama -700 offer became the best offer, and you actually clicked on that box. It didn't help that your girlfriend was yelling at you to walk your dog just as this all happened, further distracting you. Anyways, you tell her to get lost, with one eye on the game, as usual, and confirm in a hurry, not taking a careful look at your order before doing so. You just took Alabama at awful odds, and confirmed. Sucks to be you. People do this all the time, and I've been a victim before. IT SUCKS! And it's much easier to fall prey to than it sounds by my description above. People can't do this on a game with lots of volume (they need their offer to be second best, and suddenly spring to the best available), but on a game where there is typically only one or two offers up at a time (happens all the time), people lay these traps and get free money. Don't let them get yours.
I guess the underlying theme is to play small at first and go make your mistakes on $11 dollar bets, not $11,111 bets!