Consider following the example of Jeff Atwood, arguably a leader of this site:
Or you can go the extreme opposite, and add a comment for each and every revision:
Some enjoy adding hilarity to the revision comments that few others will ever discover (and thus will remain unoffended). Check out the examples in the revision history of this question and its many answers:
Question title that doesn't describe the problem
Song lyrics can be especially useful and enlightening, as are movie quotes:
Of course, if you are keen to see what others are up to (and who isn't, really?) you may find this query useful:
You can re-target it for Stack Overflow or any of the other sites. Meta comments tend to be slightly more interesting, though...