Most people use a lower grit at first to really get a good start at it so that when they are ABOUT done they use a higher grit so that they can smooth what they were doing eariler. Like at first he could use 1500 grit and work from there as that would be faster then using 2000 grit. After a while and you think you're done with most of the sanding, I would switch over to 2000 and smooth it up even more. This way you can save time and work on your part by trying to sand it with smoother grit paper.
Good luck,
Jason