That time of year is quickly approaching, and I've already been asked how to optimally create a Match list. The algorithm for the Match is relatively simple; you can look at the details on this NRMP page.
The bottom line:
1. Rank programs so that they represent your true preferences. Your first choice should be first. Your second should be second and so on. Do not try to "outthink" the system, as it will only be to your disadvantage.
2. If you would rather not match than be at a specific program, then that program should not be on your Match list. Do think carefully, however, about the prospect of not matching, trying to scramble, and possibly having to reapply next year :(.
3. If you are applying to a competitive field, consider having many programs on your rank list to increase your chances of success. How many is many? See this excellent document for evidence-based assistance in how many programs you need, depending on your specialty choice.