Having a fixed bankroll to spend definitely helps. You can also set a time limit for each gambling session. Whichever comes first.
Set the money you want to spend on that day, set your limit and your goals and dont ever chase your money back if you loose it. When you dont have proper preparation its really hard to stop yourself so you will loose money because of this, better to commit on your specific target to prevent this kind of problem.
Commit to specific target is the best one can he/she do once start gambling. And Make sure you have self control in gambling so that you know how stop playing once you win.
Some people have no control in gambling they don't know how to stop when the time they won. Be careful on gambling don't be so greedy.
Knowing your target or your limits could help you indeed to know when to stop playing gambling. It kind of addicted if you are not going to minimize the money that you are betting, the larger the lose, the more you get addicted to it, why is that? because of just one reason, of course you wanted to win it back and you are going to do whatever it takes just to get back that money that you have lost in gambling.
But it scares me to tell that not all of the people could stop whenever they want, they just can't win so easy against the urge on continuing gambling to push their luck.