Deviant art and other sites allow viewers to order prints of your work but if that is not working you need to promote your work, maybe with a stand alone online gallery.
You can print and mount them and sell them at markets.
If you make nice mounted prints cafes and stores may allow you to hang them and sell on commission.
You can sell custom artwork online. Also you can take some of your best sketches and improve them with Photoshop and sell different versions. The great thing about digital property is that it's infinitely reproduce able.
If your art is commercially valuable you may print it on tshirts, hats or posters and sell online, on the street, or sell them to tshirt makers.
Being as you're not famous I don't think your sketch book sketches in sketch book form are as valuable as they would be if you made them into hang-able art.
Even printing on an office printer and decoupaging onto pieces of wood is a cheap way to add value.