Focus on what you can control.

Your happiness is not truly dependent on circumstance; it is actually dependent on the rules you keep for yourself. If you have a rule that says you need things to go a certain way for you to be happy, chances are, you will end up unhappy since those things are out of your control and may not go the way you desire.

Let go and allow yourself to be happy no matter what.

Instructions

Tell yourself, “I will enjoy life no matter what happens.”
The next time life gets tough, remind yourself of this.
Set a rule that states you will be happy no matter what.
Instead of trying to control what you cannot control, simply accept life for what it is and remind yourself to be happy no matter what.