Here are some general guidelines to follow when creating your rank list:
Rank the programs in the order that you want to attend. This means the program you like bet is ranked first, followed by your next choice, then the next. This seems simple, but people often try to somehow "beat the system" through other ways of ranking (for instance, ranking programs in the order of what the student thinks they are most likely to match). Do not try this; you cannot outsmart the match algorithm. You are most likely to get your top choice of residency if you actually put that program at the top of your list.
Rank all programs you are willing to attend. Before you leave a program off of your list, ask yourself if you would rather scramble than attend that program. Certainly there are some programs that are such a poor fit for someone that they should be left off. This is usually rare and is likely limited to 1-2 programs per person. If you find yourself axing 5 or 6 programs, seriously consider how bad it really would be to attend these programs versus one you scramble into.
Longer is better. A longer match list means you are less likely to go unmatched. Make your list as long as possible. In general, this means your match list is the same number as the places you interviewed, maybe minus one or two programs you really could not stand to attend. Don't rank just one program.
TALK IS CHEAP. There is a reason this is in capital letters. Do not believe anything a program says about promising you a slot or placing you high on the match list. This is not because the people you are talking to from the programs are lying or trying to take advantage of you. Interviewing for residency is a lot like a few first dates - both sides are trying to look good to the other and gauge how interested the other party is. It means that what words you exchange with a program are just words. There is no assurance that anything will come from this conversation. Do not base your rank list on verbal assurances, base it on your desires for what you think is the best program for you. This is one time in life when you get to be completely selfish. Enjoy it!