The best way to control your emotions is to accept whatever outcomes you have, if you lose take a break and if you win also take a break, giving yourself a limit can help you keep yourself in control.
There are so many factors that plays a role when it comes to emotional control in gambling. Though it's not too difficult if I'm to say, because soong one is able to understand himself, then he should know when he is going out of his limits just to gamble. Loss is always a part of it, how you decide to treat your loss will determine how long you are going to last when it comes to gambling. If you take every loss to heart and get angry all the time, you will eventually end up in more losses. Don't make decisions when you are in such states.