Asking how to tune a snowboard is a little like asking how to tune a car. Performing a complete board tune correctly requires at least a couple hundred dollars worth of equipment and a certain measure of skill. Applying and scraping off wax is only about 20 percent of what is required for a full tune. Entire books are devoted to this subject and no attempt will be made here to describe the full process. There is a great little catalog from Tognar Toolworks which has nothing but ski and snowboard tuning tools, supplies and tuning instructions in it. This company use to be called The Third Hand and you can get a free copy of this 90 page gem by calling them at 916-926-2600 or go to their web site.
As for how often a board should be tuned the general rule for skis and snowboards is after every 5 full days of use. The edges should be touched up with a gummie stone after each day of use especially if there are nicks.

Here, at least, is a list of what I consider a minimum set of tools required to do a FULL tune-up:

• Screwdrivers, pliers, and wrenches to adjust and tighten bindings.
• Vise, clamp, or other device to hold the snowboard in place. This assumes you have a workbench, saw horses, or a couple garbage cans to set the board on and a suitable well lit work area.
• Pocket or diamond stone and gummi stone for deburring and detuning edges.
• Wax remover and Fiberlene paper for cleaning and removing wax from the base.
• Various files for flattening and smoothing the base and a file card to clean the files with.
• A bevel tool for filing edges and putting that perfect edge on the board.
• A rubber sanding block and carbide sand paper or a riller bar for structuring the base. THIS IS THE SECRET TO A FAST BOARD.
• Wax and a means to apply it, if you use your mom's iron you'll get wax up in the steam holes and lets just say she won't be very happy about it.
• Plastic and metal scrapers for base repair and wax removal.
• P-tex candles and ribbon for base repair and a means of applying them.
• A scotch-brite pad for removing p-tex hairs from the base.
• A plastic and brass brush for opening up the structure of the board after waxing.
  

Edge maintenance may be the most important part of maintaining your board. So to that, presented here, is a contribution from Allen Dick (dicka@cuug.ab.ca) predominantly on filing edges:

Before and after you use the file or edge tool, and between uses, take a small ($3.00 at the hardware store) stone and remove the microscopic and not so microscopic steel nicks and burrs from the edge by holding the stone flat on the bottom and rubbing up and down along the length, then do the same along the side of the edge,

This will save your clothes and skin from cuts and make your file last much longer and work much better. The burrs are really hard (work hardened is the technical term).

After stoning and before filing, take a felt pen and blacken the edge. Then you can see if you are filing flat and know when you've taken off some metal.

Sharpen the entire length. Ride it. If you find it scary, detune the six inches or so at the shovel and tail by dulling with the file *a little*.

Varsol is cheap and removes wax, but not topsheets. Be sure to re-wax soon after removing the wax so things don't dry out.

Bring your board in from the cold at least an hour before waxing to prevent lifting the base and to promote wax absorption.

CHECK YOUR BINDINGS at each tune up. Screws loosen bit by bit - then rip out! Make sure they are snug.

Get a base grind once in a long while at a shop when they have a special. A good ruler held across the surface will give you an idea whether the edges are getting high or low.

Flat is best for most of us, but some bevel the edges a bit for less 'grab' and some like a convex base for less 'catch'. I never ride entirely flat - I'm always on an edge, so I personally like a flat board.