What are some ways to decrease turbulence?
There is no way to really decrease turbulence per-se since its a factor of the air around you. There are ways to mitigate its effects and some are. 


Climb: In some cases the air higher up is less turbulent or you can climb over the weather system causing the turbulent air. In this case climbing to a higher altitude may help 
Divert: Similar to the climb situation you can divert around the turbulent air if you know where its occurring.
Timing: This is the one you may have the least control over if you are talking about commercial flying and its not always true but generally speaking the winds and thermal activity tend to be calmer in the early morning and evening. Flying around these times may allow you to find smoother air. 
Size: Again this one is hard to control but there is some truth to the fact that big planes will be less effected by turbulent air than small planes. By this I mean that a 777 is going to bump around less than a Piper Cherokee. But it holds more or less true across the board.