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.
It's all about timing! Casinos want to know that you are spending time in the casino. If you walked in the casino and lostR$1000 in 5 minutes, you may getR$5 in FreePlay next month. But if you played 50 cent bets for 4 hours and lostR$200 - your offer would most likely be higher.