Sanding

Begin sanding with a starting grit of 80 to 100 for most woods.
It's generally not necessary to sand finer than 180 grit.
Don't switch to a finer grit until the sanding scratches of the prior grit are uniform.
Use a low-angle "raking" light to evaluate the uniformity of the sanding scratches.
Remember to sand with the grain of the wood.
Don't try to sand off glue or pencil marks when hand sanding.
"Break" or lightly sand edges to prevent splintering.
Change sandpaper as soon as it becomes dull to save yourself lots of time.
Don't use a belt sander on veneer !
Sand between finishes with a grit no coarser than 200.
A hand scraper is more effective at removing mill marks than sandpaper.