Some of the tricks I've learned for improving the accuracy and track recording dependability of my GPS are as follows:
1. Let the receiver obtain and maintain a good view of the satellites for several minutes after it's turned on before saving your current position. I've found that my GIII+, eTrex's, and sportrak have a tendency to do what I call "sliding in to a fix". When you first turn them on, your reported position will often be off by a significant distance. The receiver will then drift in to your actual position. I've found this tendency to be more pronounced if there has been a significant change in your elevation since the receiver last had a position fix. I've often found my truck wasn't where I thought it should be when I failed to do wait, and tried to record my location right after I'd fired up my receiver.
2. Within a couple of days prior to trying to record a good tracklog, leave the receiver in a position so as to allow a good solid position fix for at least 20 minutes . I've found this will sometimes result in the receiver acquiring a position fix faster, and it occasionally seems to reduce errors in you tracklog when reception is a problem. What this does I'm not sure, but it appears to me to be more than my imagination.
3. With the eTrex series receiver, you've pretty much got to carry them more or less horizontal if you want good tracklogs and reception. If you don't, you'll find it looses a lock, and records track points that are off by a considerable amount. If carrying in a pocket or clipped to a belt is the way you intend to carry your receiver you'll be better off with a Quad antenna type of machine such as the sportrak. Even then you'll end up with reception problems in the mountains, and with the Sportrak, I've found it works a little better if you give it some separation from your body.
4. With a Quad Helix style antenna receiver, carry it on the side of your body opposite of the terrain if at all possible during those times when you find it impractical to carry it above, or away from your body. Not only does this improve reception potential, it reduces multipath interference which can be a problem with this type of antenna based on my experience. This style of antenna seems to be far less directional than patch antennas are.
5. On hot days, be careful about leaving your GPS display exposed to direct sunlight. I've found this can cause the display to basically go blank. You will slowly loose contrast until it can't be adjusted anymore. My old Magellan 2000 suffered from this problem the most, but my GIII+ does it fairly often at Lake Powell when on the dash of my boat during 100 degree plus days. Both my eTrex's display the same behavior, but to be honest I generally quit hiking long before it becomes a problem. Even with a water laden camelbak it just isn't fun when it get too hot.
6. With any receiver, the reception will be blocked by any solid object such as your body, mountains, buildings etc. The clearer the view of the sky, the better the odds of accurate data.
7. Don't put too much faith in the trail data you'll find on maps. Not only have I found this data to be pretty old in general, it often wasn't ever very accurate to begin with.
8. Finally, I've found that you can sometimes get better tracklogs on switchbacks if you stop at the point of reversing direction, and wait for 5 to 10 seconds before you head off the opposite direction. This almost always forces the Garmins to record a track point in auto mode, but doesn't necessarily do the same with the Sportrak.