re: Poker & PreFlop Folding Low Limit
The best thing you can do to increase your profit is probably to pick up a book. "Winning Low Limit Hold 'em" by Lee Jones and "Small Stakes Hold 'em" by Ed Miller come highly recommended - but I haven't read either of them myself (yet), so can't give you direct input.
That's probably the best bang for your buck. If you're somewhat of a beginner, you'll learn so much that after having read it, you may end up wondering how you could ever win before.
I know I've had that epiphany several times, heh.
Specifically, however, Dook is about right. You want to play ~20% of the starting hands, but it's difficult to give hard numbers, since the hands you play depend on the table you're at, what the action has been to you, your position, etc.
But, seriously, invest $30 in a book. You'll never regret it.