Prolimatech's website FAQ recommends to 'please spread out evenly a thin layer of PK-1 onto the whole CPU and to the whole heatsink base bottom.'
Based on their recommendation I assume the following method is appropriate:
To apply; simply heat the tube by running under hot water from the tap. Wipe it dry.
Get the thinnest plastic bag you can find (freezer bags are ideal), and cover your hand.
Apply a rice-grain size of the warm paste to the centre of the CPU heat spreader. Holding the CPU in one hand, GENTLY rub the paste using a circular motion, across the surface with your index finger (through the plastic bag). Just use VERY light pressure and massage it in until the surface is covered completely.
After rubbing for about 15 seconds, the heat from your finger softens the paste and eventually, it leaves behind a nice thin haze on the heat spreader.
Wait one minute and repeated the process to get a slightly thicker coat and then do the same thing to the bottom of the heat sink.
There are other methods I can try like dot, line or x-method.