How to get good coordinates (when hiding)
Many cachers complain when they find a cache and the coordinates are 75 feet away. To help prevent this from happening to your caches, use this method:
step one Walk up to your cache and hold the GPS as close to it as possible without blocking out too many sattelites.
step two Wait for 3-6 minutes without moving your GPS, then take a mark.
step three Repeat steps 1 and 2 after walking away and coming back from several different directions.
step four Repeat all the steps on a day with different weather
step five Go back to your cache and, after waiting several minutes, find out which waypoint is the closest to the actual location.
step six Repeat step five until it becomes obvious which waypoint is actually the closest to the cache.
If you are not that much of a perfectionist, then you can skip step four.
Some tips for getting good readings
If the cache is in an area with very bad reception, go into a nearby area with good reception, get a good number of sats, then walk in a straight line toward your cache before taking a mark.
Always wait at least 2 minutes before taking a mark, even with lots of sats. This way, the GPS has time to average the signal from the sattelites and get more accurate coordinates.
Read the users manual. They should tell you how to hold your GPS to get better reception. For Magellans, at least, you should hold the GPS vertically, so that the top is pointing up.