There are three factors that any basic slot players need to keep in mind when looking to stretch their bankroll are:
1) Avoid multiple pay lines and stick with single pay lines. The multiple pay lines machines are too expensive. If you are going to play multiple pay line machines make sure it is a bonus slot machine that offers a bonus round that you can win additional money.
2) Stick with two coin maximum machines. Sure a three coin machine offers more money but you also had to gamble more money to play. Remember you are looking to stretch your play and really the more pulls you can make the more chance you have at winning. For every 2 pulls on a three coin machine you would get 3 pulls on a 2 coin machine.
3) Find and play the machines that offer double jackpots. These machines offer double jackpots on specific pay-line combinations. Make sure you read the machines payout schedules as all machines are not created equal and you need to know when you should be winning double and when you shouldn't.