The Ugga Bugga slot machine game has the highest payout percentage, at 99.07%. The second highest is Mega Joker by NetEnt, with a 99% RTP. Jackpot 6000 by NetEnt and Uncharted Seas by Thunderkick come in second and third, with RTPs of 98.8% and 98.6%, respectively.
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.