Last year I wrote letters for two students who each applied to only two schools. Those programs extended their best fellowship offers to those students partly because they knew the odds of either of those students accepting were good. Keep your list short, even if you don't think you're a contender for a top fellowship. Probably no more than six, and certainly fewer than 10. Applying to a dozen programs carries a whiff of desperation or lack of focus.
Professors are busy people, and registrar's offices are overworked bureaucracies.
Check with all the departments to which you applied to make sure their file on you is complete before the January deadline. In the end, the best way to avoid costly mistakes in the graduate admissions process is to let your own maturity guide you. John M. Torkelson, Ph.D., is associate dean for graduate studies and research at Northwestern University's Robert R. McCormick School of Engineering and Applied Science.