Don't make eye contact with the pit or dealers. Smile a lot when people are winning. Mutter to yourself. Talk to someone standing near you. Recount the dealers total while he takes everyone's money, then shake your head in disbelief. Recount the dealers total when he's paying everyone and shake your head in disbelief. If someone win's a big bet, count his chips to see how much he has won. Point whenever someone gets a blackjack and yell "Touchdown!"
The point being, you need to look like you're interested in the game and are thinking about playing, but you're just not ready at the moment. You might be new to the game, or you might just be another wierdo in the casino. Don't stay in one place too long or you will come to be known as "the guy waiting for a hot shoe."