This guide is best used by newbies, as it only gains you very few np. It probably wouldn’t even make the site!
Anyway, go to the shop wizard and look up the bottles of sand. As you can see, they are only 1np, but have no use at all. If you buy these bottles of sand, and sell them on the auctions for 1np starting, 1np minimum increments, and 1 hour auction time, you will gain at least 1np per bottle of sand! It is only about 8np(because you are limited 8 items up for auction at a time), but it is still gaining.