Three pair is quite a good hand in pai gow poker.  Fortunately, there is only one way to play it - put the largest pair in the 2nd high hand.  Period.  No exceptions.

Let's look at just one example:

Given the following        set your hand.

Always put the largest pair in the 2nd high hand

2nd high:  

High hand:     

That's all there is to it.  Good luck!