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.