>>>I can't get a fix.
Trees, cliffs, and canyons can all block reception, especially when you're using a less powerful receiver. Your best bet is to move higher or out of the trees. Another option: an add-on antenna.
>>>My map and GPS don't agree.
Your map plot may be bad, but it's also possible that your map datums don't match. Look on the lower left corner of your printed quad. If it says 1927, and your GPS is operating off a 1984 survey, that may explain the variance. Select the correct datum in your GPS's setup menu. If you're not carrying maps, use the GPS's default setting.
>>>My GPS compass isn't lining up with my magnetic compass.
If you're holding them near each other, metals in the GPS may be pulling the magnetic compass off. Not the case? Make sure they're both set to either magnetic or true north. Still doesn't work? Recalibrate your GPS's electronic compass. (You must do this every time you change batteries or lose power.) When in doubt, you should always rely on the magnetic compass.
>>>The pointer keeps changing directions.
Trying to follow your screen pointer in dense timber can send you on an erratic course, since poor reception can slow down position updates. This is particularly true after a rest break, when the GPS can't guess your previous direction. Just get going on the route you were following, and check with the GPS in a minute or two.