The best ways to keep the 360 cool are:
1) Do not stack it ontop or beneath any other AV equipment (or equipment that produces heat)
2) Do not block the vents
3) If you put it in a entertainment stand, make sure that it is not fully closed.
4) Do not buy an intercooler, MS says that they can melt to your 360.
What is the best way to keep your xbox 360 cool.