Oh, seperate note on maps... note the datum the map is in, and (if you use a GPS) the datum that the GPS is set to. If they are not the same, you will probably mark yourself in a different location on the map than where you actually are.

If you don't understand why different datums can result in positional ambiguity, this may help: http://www.colorado.edu/geography/gcraft/notes/datum/datum.html