Get a book or take a class....The two "classic" books are
Wilderness Navigation: Finding Your Way Using Map, Compass, Altimeter & GPS, 3rd Edition (Mountaineers Outdoor Basics)
I have this and its ok...I found it to be a bit over thought and poorly organized as a book to learn from. It has good information though
Staying Found: The Complete Map & Compass Book
which I have not read. Both are available at the usual outlets
REI carries this one...I have no particular opinion but NOLS is probably a good source.
There are lots of others