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Aim for a slot machine that pays out on average at 95% or more, the more it pays out, the better for the player.
Understand the way the slot machine works in order to understand potential winnings. Understand odds and all of the different combinations will help players to determine which is the best bet to make to try and achieve maximum profit in the long term.
Be strong when it comes to setting a bankroll. Players do not win every single time they play. It is important to imagine a bank roll and stick to that figure so that losses to not spiral out of control.
The general rule of thumb is to try and keep playing when winning, but slowly remove some of the winnings. Keep betting similar amounts and slowly withdraw some of the winnings. This ensures that a bankroll is still present, but profits are taken as well, which is the best way to earn on slot machines.
Try and go for the maximum bet in terms of coins, but try and keep to a small coin value. This will give a play a much better chance of winning in the long run.
Try and find a machine that suits style of play and paticular bankroll. For instance, if you have just $20 then it is likely to want a low stakes machine with a high win percentage.