it only needs to be a very small amount, putting too much on will have the opposite effect to what is needed, you need a very thin layer placed on the chipset die, then spread it out with something like a credit card or plectrum. put the heatsink on and move it around a little bit, to spread the thermal compound around otherwise you may only get it in the centre. thas about it really, oh and what are you using to get the old stuff off? 99% isopropyl alcohol is excellent for that.