when applying arctic silver or comparable thermal goo i'd suggest using a business card to smooth it out before plopping the heatsink in it...you only need a layer about 1/64 inch thick for good thermal conductivity.
but he is correct about AMD voiding warrantys due to thermal paste evidence, so think before you goop it.
if you think your stock hs has trouble fitting ill show you how my 80mm ax7 fits, its a goddamn miracle it fits over everything on the board...
Insert CPU and lock it down.
->
Apply thermal grease as needed, smooth with credit card or simmilar.
->
Mount heatsink on cpu, secure one side of the clip, preferably the back(non cpu lock side/no pusher), then with a narrow screwdriver push and move the clip into place over the tab.
A friend of mine didnt know to take the sticker off the heatpad on his hs the first time he built a computer, his system ran fine...smelled like ass though.