you need to completely remove all traces of previous thermal compounds, whether they were pads, grease or whatever, before applying any new one.
the cpu should have a thin, even, smear of thermal compound, only on the 'core'.
the heatsink should have been prepared by rubbing in some thermal compound with a 'lint free' cloth, then rubbing it off, with the same.
Bringing together the heatsink/fan assembly & cpu should be a single operation - lateral movement should be avoided, the aim is to embed the heatsink in the compound on the cpu core, such that maximum thermal contact is achieved.
deep breath - flat head screwdriver - click
