What to do if you become lost at a hike

Most of the cases where people become lost was a result of them going off the trails. It is therefore crucial that you stay on the trails and notify the tour guide when you desire to go off track.

The Number One tool needed for survival when you are lost or injured in the wilds is a Positive Mental Attitude. You should continually tell yourself that you have to get home. When you panic or lose hope, the situation becomes fatal.
The Number One thing you should have done before you got lost is something you should have done before ever stepping on the trail. Leave Your Hiking Plan and expected return time with someone, they can report you missing if you do not check in with them at your return time. If you also left this information with a ranger at the trailhead, they'll know quickly when you are not back.

   

STOP - As soon as you realize you may be lost, stop, stay calm, stay put. There is nothing you can do about whatever got you to this point - all you can do now is solve the problem of getting out of the situation. The further you walk, the longer it will take rescuers to find you. If you don't know where you are, walking further has at least a 75% chance of being the wrong direction. If you are not safe where you are, then move to someplace safe and stop there.
Sit down, take a drink of water, eat a handful of trail mix, and relax while you think things over.

THINK - Go over in your mind how you got to where you are. What landmarks should you be able to see? Were you heading North or West?
Do not move at all until you have a specific reason to take a step. Walking around while thinking is not good, sit on a rock or log while you observe your surroundings.

OBSERVE - Get out your compass and determine the directions from where you are currently sitting. Using your map and the general area where you are, identify landmarks that you should be able to see. This step is often enough to get re-oriented and sure of where you need to go to get back on track.
Consider your situation. Estimate how long you have until dark. Check out the weather and determine if it looks like it will be getting better or worse. Check your water and decide how long it should last. Consider the other hikers in your party and how they are doing when you plan your next steps.

PLAN - Based on your thinking and observations, come up with some possible plans and then act on one of them. Prioritize the needs of your group and deal with them in turn.
If you are confident that you have determined the way to go and have time before dark to reach a known spot, such as the marked trail on your map, then go carefully and obviously mark your route with stacked rocks, sticks stuck in the ground, or strips of cloth from your bandanna.
If you are not very, very confident in the route, then its better to stay put.