Sanding to stain is like primer is to paint. If you do a great job at sanding no one notices, BUT if your sanding jobn is minimal and weak - they will notice! No finish will hide a bad sanding job - same applies for prep and primer work prior to applying paint on the wall.
*Always do your sanding in a well lit area - it is easier to see scratches, nicks, dents or glue marks.
*Don't press too hard while sanding, keep even pressure if using a sanding tool. You do not want to dent into the wood from too much pressure.
*Sanding is not only a one step process. Sand out all blemishes which is any deep scratches, nicks or dents. Use a course grit such as 120-150 for the first layer of sanding.
*Sand in layers and sand with the grain of the wood. Change your paper often-be it on your tool or hand. The sanding does wear out and you will have uneven areas if you do not change papers often. Work your way up in sandpaper - ending with 320 grit.
*Your final sanding should be with the 320 - be sure to sand all of the parts with each sandpaper - including back ledges, legs and corners. You can wrap the sandpaper around the edge of a putty knife to fit into the back of a ledge on a table or dresser.