Read the Paytable/Payback Percentage: All slot machines are required by state law to display the payback percentage somewhere on the machine. These are often displayed as a sticker and are not always easy to spot at first glance. Obviously. the higher the percentage, the higher the payback.
Play the Right Machine: There are 2 major types of slots, progressive jackpot machines and standard.
You are only eligible for the progressive jackpot if you are playing the max coin, so if you are not playing the max bet you should stick to the standard machines.
The reason for this is that if you are not playing for the jackpot, then you are actually playing below the payout percentage. When you are playing the progressive machine, a percentage of every coin you play is being pooled in the jackpot and you are not eligible to win it back unless playing max bet.
Check the Candles: A way to save you some time when you are looking for the denomination you want to play is to look for the lights on top of the machines.
These are often called candles in the casino business. The bottom light on the candle represents the denomination. In most casinos, blue represents a dollar, yellow is for quarters and red is for nickels.