Read the map regularly. Sure it sounds obvious, but many hikers look at the topo only when they're lost.
Visualize the terrain ahead based on the topo's contour lines. If the area doesn't look as you imagined, verify your location on the map immediately.
Know your pace so you can calculate the time it'll take to get to a landmark. You'll be tipped off if it takes unusually long. Figure out your pace by timing how long it takes you to hike a mile wearing a pack.
Use a compass to verify your general direction and orient yourself with the map, but don't expect it to tell you where to go. You have to study the map for that.
Never wander when you're lost, and always keep a level head. As soon as the landscape doesn't jibe with your map, backtrack to a place you can clearly identify on your map and start over.
Daydream later. Keep track of the terrain you're traversing, as well as any changes in direction.