The truth is that there is no trick to slot machines. They provide random results based on set mechanics and it all comes down to luck. With that being said, not all games are the same, so picking the right options is key, and you can still change the size of the bet throughout the session for better results.
First is to always play max bet. Second is to play the highest denomination you're comfortable making the max bet on - quarter slots tend to pay better than penny slots; dollar slots tend to pay better than both; and so on. Third - and this is the big one - remember that every spin is an independent event.