i don't know how accurate it is, but im assuming it has a thermal proble. for amds, just stick it somewhere on the pcb. For intels, if you want to remove the heatspreader, do that to get the most accurate reading. Second best would be on the side of the cpu, or finally you can stick it onto the heatsink. it should come with some special tape to allow you to do so.
hey, i know im not doing a very good job describing, maybe someone else can do better, but maybe when you get your parts you will have a better idea. you might want to stay away from removing the heatspreader if you have an intel unless you aren't afraid of ruining your processor.