Make sure after you load an article of clothing, go to the figure drop down menu, select conform to and conform that clothing figure to the character. This is the starting point.

There are then three broad catagories of fixes:

1. Sometimes you need to adjust the size of the specific areas on the clothes where the character is sticking through, this is done by spinning the dials in the parameters menus for the clothes,

2. sometimes you can just make that part of the character that is sticking through not visible, this is done in the properties menus for the character, it is a simple checkbox

 3) and often, for small pokes, it is just easier to fix the poke throughs in postwork after you have rendered your scene.

Go to the tutorials section of RMP and type in "poke through." There are several good lessions for how to fix this common problem.