In slot games, everything is pure random. You can win or lose even if play strategically since each bet is independent so there’s no strategy you can apply to increase your winning percentage.
All you can do is to rely on your luck and manage your bankroll properly so that you will not over committed on playing slot games that will give you huge loss once you encounter no winning at all despite playing many spin.
So you’re right on your first suggestion that you should stop if you already can’t concentrate on the game.
Correct, what we can do when playing slots is to choose the slot game with the best RTP (both live RTP and its default RTP).
As well as choosing slot that give a better chance to win big multiplier not only in free spins/bonus round but also in normal spins.
Testing the air is also good to do, something like playing 100-200spins to decide whether the slot is in its good mode or not.