If you too prefer to not have your book collection marred with price stickers or just have a vendetta against labels in general then this is the Instructable for you. This is the method I prefer as it is can be quick and most of the time there isn't a whole lot of mess to clean up (no guarantees).
sandpaper - 120 grit (or other coarse grits)
"label lifter" or plastic scraper**
paper towel/toilet paper
latex gloves (optional but recommended)
*I would think any lighter fluid would work but I find Ronsonol Lighter Fuel works best and is the cheapest (the one in the yellow bottle with blue on it), but I have had satisfactory results with Zippo brand fuel too. I guess you could also use Goo Gone but I personally can't stand the smell and find it's messier as it doesn't evaporate as quickly as most lighter fluids (not really recommended).
SAFETY NOTE: Lighter fluid contains naptha which can be dangerous to your skin, lungs and other important parts of the body. I would recommend wearing latex gloves and work in a well ventilated area. For your reference, the MSDS for Ronsonol Lighter Fuel: http://www.cooperbooth.com/datasheets/160606.pdf
**I have a Goo Gone label lifter that works great but you could easily make a scraper out of a credit card by scraping a beveled edge (like that of a chisel) by running a utility knife along an edge at an angle a couple times.
Step 1: Test the Resistance of the Label
If it doesn't peel off easily move on to Step 2.
1. Be careful of removing labels from book covers with a glossy finish without using the lighter fluid method, they sometimes come off easily but take the glossy coating with it and leave a dull area where the label was. It's usually unnoticeable but if you're like me, once you notice it you'll see it every time you pick up the book, for the rest of your life.
Step 2: Scuff the Label With Sandpaper
Use your piece of sandpaper and CAREFULLY scuff the label without getting too close to the outer edge of the label (you risk scratching what's underneath the label if you do and it's usually not necessary as the fluid will seep underneath the label perimeter from the outside edge). Also be careful not to scratch too deep and tear right through the label, you're only trying to break through the nonporous layer enough for the fluid to seep through.
Step 3: Saturate the Label With Lighter Fluid
Let the fluid sit for a minute or two to do it's thing and evaporate (you can try to peel it off when it's wet but I find it is then more likely to leave adhesive residue). The fluid tends to drip all over the place so be sure to keep your paper towel standing by.
2. Be sure to first test an area on the item to see if the lighter fluid will ruin it in any way (remove coloring/dissolve it). Most papery products like book covers might slightly soak up the fluid but will be fine after it evaporates (again, no guarantees). The fluid tends to shoot out of the bottle pretty quickly so you could try holding a finger over the nozzle to get more control on the flow.
Step 4: Remove the Label
Slowly peel off the label.
3. Some labels are stubborn and don't like to come off in one piece even after a second saturation of lighter fluid. In such a case it's best to just tear off what you can of the label and then repeat Step 3 or just add lighter fluid and work the scraper while it's still wet. Also, if you peel off a label and the label comes off but the adhesive doesn't, just drop some lighter fluid onto the adhesive, let it sit for a couple seconds and then scrape the saturated residue off and wipe clean.