http://www.tomshardware.com/reviews/thermal-paste-heat-sink-heat-spreader,3600.html
Complete walk-through. Just skip to the thermal paste application part or use my advice below:
1) Observe the proper orientation of CPU to mount
2) Drop processor from a few mm's then jiggle slightly to ensure it's seated
3) Lock the CPU in place (read CPU manual if needed)
4) Use a pea-sized amount of paste (about 4 to 5mm in diameter)
5) Don't spread, just place the CPU cooler on top (there are different methods. I use this one)
6) Screw in the CPU cooler. Do each screw a little at a time. Start with any screw, then choose the one at a diagonal to it then the remainder then repeat.
To test:
1) stick with DEFAULT BIOS settings even if going to overclock later
2) choose optimal DDR3 memory settings (AMP? forget name in BIOS)
3) run MEMTEST www.memtest.org
4) in Windows run Prime95 and/or other CPU programs.
5) setup FAN CONTROL using the motherboard software. Make sure it's varying the speed by running at max then forcing to 50% (will want it to "ramp up" as needed)
6) run "coretemp" and/or other programs to observe the temperature under load (use the highest core temp)
http://www.alcpu.com/CoreTemp/
*You want the highest temp of any core to be lower than the Tjmax of the CPU.
Other:
1) Note that Prime95 stresses the CPU more than a program ever would so if you stay below the max temperature here you'll have no issues.
2) update the BIOS if newer exists.
3) always run MEMTEST again if you change the CPU or memory settings. This includes updating the BIOS.
4) If overclocking, run MEMTEST, then Prime95 with Core Temp.