I use two boards to clamp the saw in the vise, with the tops of the
boards just a tad higher than the bottom of the teeth. When I file
the teeth, it leaves a score mark in the boards. The score marks keep
track of what teeth have been sharpened, so you don't miss one, or do
one twice, or do the wrong tooth. It's also easy to keep the filing
parallel as you go by keeping the score marks parallel. When you do
the other teeth, the score marks are easy to see because they are at
an angle to the first set of teeth.

First path looks like this: / / / / / / ... marks for every other
tooth.

2nd path looks like this: /\/\/\/\/\/\/\/\/\... easy to see none were
missed.

Hope this helps.....