As long as you have more than four chips left, continue betting one unit at a time. As soon as you have a losing round, start back at the table minimum. Quit and take a break if you lose three times in a row. If you get five losing spins in a row, move to another machine. Chances are the one you're on is in a cold cycle, or it's set for low payback to begin with.
All machines go through hot and cold cycles.
If, after 5 or 6 hands you haven't hit payouts that come even close to the total you've put into the machine, move on. Watch the meter. Once the count grinds down and is 40 coins below your highest total, cash out. You're a true winner if you leave the casino with more money than you came with. It's greed that keeps people at a table or a machine too long.