I checked out this website laymansgablingguide.com and found it has a lot of good information on slot machines.  For one thing it tells the pay outs that slot machines usually pay.  If the machine says it has 90% pay out that means for every $100 it collects, it pays out $90 at random intervals.

Remember slot machines are games of chance.  Slots are not going to make you rich. Another point on the website slots can be seen as a form of entertainment and fun, just don't spend the rent money.  There is no way to determine when the machine will payout the big bucks.

The site also has some good tips on does and dont's for playing the machine.  The most important is to set aside a small amount of money to play the slots with, when it is gone, it is time to go.