If you have an edger, use it to ease the top and bottom edges of the belt or notebook.  If you don't have an edger, use some 60 or 80 grit sand paper to sand the edges into a rounded shape.  IF you want a smoother surface,  use a finer grit. You can burnish an edge that is not rounded, but the rounded edge looks better. Dampen the edges with some plain water - use a sponge, spray bottle or a rag.  Now rub the edges with something hard and smooth.  Use an antler tine, a smooth piece of wood, a ball point pen,  a bone folder, etc.  (Many tools are available commercially).  Continue to rub briskly the entire length of the item.  Soon you will notice the edges getting smooth.  If you have some saddle soap - either the cream or bar - rub some on the edges.  Many people prefer saddle soap and water to just plain water.  Now, use a piece of canvas, blue jean material, or other coarse cloth and dampen it and add some saddle soap.  Rub very fast and hard along the edges.  You will see a nice smooth edge develop.

The combination of heat from the friction and the pressure of rubbing will smooth the edge.   There are lots of other lotions and potions people use.  Try several and decide what you like.  Many people use Gum Tragacanth in place of the saddle soap.  I have had good luck with several of the "all in one" cleaners and polishers.  

Now, wait until the edge is dry and then rub it with a bar of paraffin.  Briskly rub the edge with a coarse cloth until it is smooth once more.  The wax will keep the edge smooth longer than plain water or water and saddle soap.  There are many other edge products available.  Try some and remember to keep notes. If you want a dyed edge, use the dye before burnishing.  The saddle soap and/or wax will make a dye job difficult, if you burnish before using dye.

NOTE:   Don't work over a carpet!

Phew, lots of work, but wasn't it worth the effort?  A plain, raw leather edge is fine in some cases, but a nice rounded and burnished edge makes your work look and feel more professional.  And some people wonder why good leather artists charge the prices they do.  This is only one example of the time and effort that goes into a fine piece of leather work. 

Many Leather Workers use paint (usually Acrylics) to cover their edges.  Often the first coat will raise some leather fibers. Lightly sand the painted edge with a fine grit paper and repaint.  This will result in a colorful edge.  Tandy has a new line of colored edge treatments by Fenice.  They are certainly worth a try and many colors are available.  No, Tandy doesn't pay me to say nice things about their stuff.