I used this guide here.
I used the 12" x 12" tile you see in the picture and pushed it all the way to the top and pulled it all the way down (full strokes). If I had to do it all over again I would use 220 to start sanding the HSF. The metal is much harder to work with and 400 was a bit to fine. I had to use the whole pack to get it flat. 400 grit is the perfect place to start on your CPU though.
Hint: You won't find higher than 600 grit sand paper at your local Home Depot or Lowes. You will need to go to a Auto Parts Store
. Autozone had up to 1000 and O'Rielly had up to 1200/1500/2000, the latter two where "upstairs" in storage and I had to ask for them.
It takes 1500 at least to get a mirror shine and 2000 will just be overkill SUPER shiny (which you mind as well do after 4 hours lapping). I personally enjoyed learning to lap. I was hesitant at first but buy the time I was done I was quite comfortable.
Tip: Use full strokes the length of the sand paper and rotate 45 degrees every 30 secs or so (usually 10-15 passes). I drew a cross on both before I started and made sure I was keeping it flat through the whole back/forth motion.
You will start to notice when it gets flat because the sanding streaks will run across the full
surface in whatever direction you are sanding. When it is not completely flat yet you will see different patterns, indicating that the sand paper hit different sections of the surface at different times.