From my tutorial, which I do not claim is the best, or most accurate, or even "right" for every application, but you certainly won't go WRONG by following it.
Prior to establishing the mounting pressure you'll need to have already applied your thermal paste and although opinions regarding the correct amount vary as widely as you can imagine, the old adage about opinions being like a very distinctly distasteful body part would certainly seem to apply here. Everything from five very small dots to slathering it on with a credit card, using a pea sized dollop, the three line method and possibly anything else up to and including drawing a smiley face have been not only mentioned in various circles but almost certainly tried in reality as well.
-Some methods "Recommended" around the web-
-The likely, but undesirable results of those methods-
I don't recommend any of those, and to clarify, I'm not claiming to be an authority or trying to indicate there is no other way but mine, but it is one that has worked on literally hundreds of builds over the years without issue.
I personally prescribe to the large cooked rice grain (For high mounting pressure type heatsinks) or a dab about half the size (Of the part that sticks past the metal) of a #2 pencil eraser (Low mounting pressure type heatsinks) when using any of the commonly available pastes that come in a tube applicator like the Arctic Silver 5 or most of the included pastes that come with premium coolers. If you are using a stock, low pressure mounting system type cooler like those which use the stock mounting hardware and backplate, you will want to probably use double the amount of thermal interface material (paste) because the low pressure will not effectively force the paste outward from the center point nearly as much as aftermarket high mounting pressure coolers do.
I've never had excess paste squeeze from between the CPU lid and heatsink using this method nor had an issue with inadequate cooling due to any lack of sufficient TIM. You can make your own decision on what works best for you. Depending on the cooler, a very small snow pea sized dab will work well too, so long as you don't get carried away or misconstrue the definition of snow pea. For our purposes, perhaps a dab about 1/3 the size of a number 2 pencil eraser is a better description.
-More promising methods-
-Probable results-
Notice that even with this method there is substantial filling of the heat pipe seams. It is NOT necessary to lay multiple lines along seams.
Nearly every novice builder thinks more will be better, until they learn for themselves how wrong that way of thinking truly is. The paste is only there to provide a thermal interface between the metal of the cpu lid and the base of the heatsink. It's only job is to bridge any convex or concave tendencies of the lid or heatsink base and to fill microscopic pores in either surface.
It's not there as a magic cooling pad and it's use would actually be entirely unnecessary were both surfaces to be completely flat and non-porous. But since that is unlikely, a thermal interface material is required.
(As home mechanics, handymen, tinkerers and especially with guys in general, we tend to want to always do a little extra. An extra turn on that bolt, which causes it to break. An extra half gallon in the gas tank, which overflows and slowly eats your paint away.
The list goes on but in this instance you'll want to to avoid the inclination to add any "extra" or "just a little bit more" when applying the paste. One small strip in the dead center, the size of a large cooked grain of rice or two small uncooked grains of rice at most, dead center, is plenty to fill the needed areas when the heatsink is tightened to the correct specifications using the recommended tightening procedure.)