Get a heavy grade file since the file should be used for tough jobs that the sandpaper cannot tackle. Also, do not forget to have some clean, lint-free rags around. If you get any lint in your wax, your ski tuning will not go so well.

I.  SKI INSPECTION
  A. Evaluate the skis
    1.	Are they flat, convex, or concave?  A true bar will help determine this.
    2.	Check for gouges or scratches.
    
II.  CLEANING
  A. Begin with damp paper towel and wipe ski clean.
  B. Remove wax and grit with Ski base cleaner.  Let dry approximately 20 min
  C. Do not clean the ski with a scraper; it can force grit particles into the base material.
  D. Be sure nicks and gouges are clean of wax and grit.

III. BASE REPAIR
  A. Nicks scratches and surface gouges can be easily repaired with P-Tex.
  B. More Serious gouges should be done with the proper equipment.
      P-Tex gun or plastic  welder or by patching.
      This should be handled by a repair shop or ski shop.
      
IV.  BASE EDGE SHARPENING AND FINISHING
   
  A. Go over bottom edge with file to put a 1,2, or 3-degree bevel on base edge
    1.  0°-1° = Slalom or Recreation
    2.  1°-2° = Giant Slalom and downhill
    3.  2°-3° = Downhill, speed skiing and Ballet.
  B. Use a 3°sleeve over tips and tails instead of rounding off edges.
In Tool Tips: Precision Tuning Guide at FKtools-us.com they say:
  - Hard pack or ice: bottom flat, side 1 deg bevel
  - Soft snow; bottom 1 deg. side 90 deg.
  - Torsionally stiff or tough turning ski:  bevel the base
  - Bevel both the base and side edges to the same angle to reposition your
  90° edge for smoother easier turns plus a good biting edge.
  
 V.   SIDE EDGE SHARPENING

   A.  Gives you the ability to grip and hold on firm show conditions
       Recreational skier 90° 
   B.  If you bevel side edges you can increase gripping power.
 
 VI. EDGE FINISHING OF DEBURRING

   A.  Edges need to be de-burred before waxing.  We de-burr because de-burring 
    removes the thread of steel that is produced right on the comer of the 
    edge that makes it feel excessively sharp.
    A coarse DIAMOND file is used to polish and remove case hardened burrs and
    will help restore the factory finish AFTER your file tune.
 VII.  DULL TIPS AND TAILS
VIII.  WAXING

    A.  Waxing enables the skis to glide and turn more easily
        as well as protect them from damage and wear. 
Source: The Basics Of Ski Tuning (Word Doc) at NAVA Ski Club 
 __________________________________

To find the dulling zone on YOUR skis:

1. Locate the widest part of the shovel. The edge between this point and the tip should have the edge sharpness removed.
2. Locate the widest part of the tail. The edge between this point and the end of the tail should have the edge sharpness removed.
3. Place a permanent mark on the sidewall of the skis at these points as a reminder - this marks the junction point between the turning and the non-turning zones of the ski. Dulling edges beyond this point will reduce the performance of your skis (that is why it's called detuning).

Tognar Ski Snowboard Edge Polishing Deburring Tips:
Deburring is the process of removing rough burrs from the side and base steel edges of skis or snowboards every time you either file 'em or after a day of ridin' 'em on the slopes. It's done with a deburring stone. This helps keep edges smoothly sharp, and free of nicks, rust, raggedness and roughness. Compared to personal hygiene, it's somewhat akin to brushing your teeth. Dulling, on the other hand, is more like performing a lobotomy. It's usually done on new skis or boards with a file and/or deburring stone to intentionally dull (or radically bevel) base edges at the very tip and tail where skis and boards lift up out of the snow. Edges here curve dramatically in toward each other, and should be addressed so they don't unexpectedly engage in bump troughs, ruts, crusty snow or other funky condition to revector your planned line of travel downhill off in some new, wild and unanticipated direction.Yikes! Detuning refers to the subtle "massaging" of an edge's sharpness or base bevel near tips and tails to intentionally adjust performance of a ski or board. On old traditional skis, detuning behind the contact points made a skis less grabby and "hooky" for easier control...but detuning a shaped ski can make the ski more "nervous" due to shortening the effective running surface, plus the skis won't initiate turns as desired due to the decreased radius and running surface. So for shaped skis find the contact point of the tip and tail (you can do this by placing the ski on a flat surface and marking the sidewall at the points that the ski contacts the flat surface) and detune from contact point forward on the tip and contact point backward on the tail.

Links:
Tognar Toolworks tuning tips and products
Tool Tips: Precision Tuning Guide at FKtools-us.com
The Basics Of Ski Tuning (Word Doc) at NAVA Ski Club
TelemarkTips.com/EdgeTuning.html
Tognar Ski Snowboard Edge Polishing Deburring Tips
Understanding Tip/Tail Dulling