It’s always good to know where you are. If you’re hiking on trails, here are the techniques I use to keep track of where I am at all times.

Have the best trail map available
Locate, purchase, and carry the most detailed, up-to-date, and accurate trail map for the area you’re visiting. Whenever possible, spend the few extra dollars to purchase a waterproof map made from plastic (good) or Tyvek (the best) for their resistance to wear and tear.

Fold your map to cover the area you’re visiting 
Don’t fold and refold your map repeatedly as you go, which is a hassle and starts to wear out your map along the creases. Fold it once so that most, if not all, of the area you’re visiting is face up. And don’t be afraid of creating new folds in the process—this actually helps preserve your map over the long-term by avoiding over-use along the existing folds.

Keep your map in a zip-lock bag or map case 
This protects it from wear-and-tear and, if it’s paper, keeps it dry. Zip-lock freezer bags are the thickest and most durable.

Carry your map in an accessible spot as you hike
Don’t keep it somewhere that requires you to take your pack off to access it, which all but ensures that you will rarely reference it. A deep pocket on your hiking shorts or pants or a pocket on your pack that you can access while wearing it are both common options. (I wear nylon hiking pants with a large and deep side pocket for just this reason.)

Reference your map regularly
Follow your progress and mark your location as you go, especially any time you reach a known landmark or trail junctions.

Know your pace of travel
Develop a sense of how long it takes you to hike a mile over different terrain, which allows you to estimate your approximate location based on the time you’ve traveled from your last known location.  For example, I know that it takes me about 20 minutes to hike a mile on gentle terrain, increasingly more over steeper and rougher terrain.

Monitor the direction and steepness of the slopes around you
Staying aware of the angle and direction of surrounding slopes can help you refine your location on the map, especially in areas like the Northeast that feature a lot of topography.

Know your elevation
One of the most useful tools I use to identify my location is an altimeter watch. When you’re hiking on trail, knowing only your elevation (and the trail you’re on) is often all you need to pinpoint your location. (This information is not very helpful on long, level stretches of trail, but such sections are definitely less common.)

Keep tabs on your general orientation
On sunny days, you can keep track of this as you move by monitoring the sun’s location. On cloudy days you’ll need a compass. This is helpful to ensure that you’re hiking the right direction on the right trail.

Use a GPS and plot your location on the map
Of course, knowing your precise coordinates makes it easy to pinpoint your location on a map, but it does take a small amount of time and hassle to do so. If you’re carrying a GPS unit, by all means use it from time to time, but consider it a secondary tool to the skills and basics outlined above.