1

Looking at a slot's return to player (RTP) percentage. For those hoping for a speedy return on the bulk of their spins, the RTP % of the game is all they need to know. ...

2

The slot's volatility. ...

3

Tournaments of slots.

1

Read the label. Some slot machines (not many) have their theoretical RTP printed somewhere on the machine itself.

2

Google it. Slot manufacturers sometimes post information like payout percentages on their websites.

3

Get comfortable with averages. ...

4

Use actual results.