The way you pull or push a file can be called the draw. You can draw away, or towards your body. There is no right or wrong direction. Personally I prefer to file base edges with an away draw, and file side edges with a toward draw.
In a perfect world, one could file both base and side edges with a draw direction of tip to tail only. They could do this by utilizing both push and pull draws with the same hand, or alternating between right and left hands.
Files are to be used in one direction only. If you do not lift the file completely off the edge, on your back draw, you will dull the file prematurely, and will either case harden the edge that you are filing, or dull the edge you originally intended to sharpen . This post does not refer to use of diamond or creamic stones as they can be used bi-directionally.(not a gay joke) haha
Case hardening can also be found in the tips and tails of factory tuned newer skis, and commonly on older skis under foot in rock damaged areas..
If you you have a case hardened area of edge where your'e filing, the file will "zing" or skip over an area that may look polished, but will difficult to cut into with a file. If you alternate between a coarse'ish diamond/ceramic stone, and a file, you can eliminate the case hardened area eventually.
hope this helps.