In an ordinary lost situation if you did the right thing & notified several people in regards to WHERE you were going & WHEN you intended to return, then all you have to do is sit tight & wait for someone to find you. This is of course providing you STOP as soon as you realise that you are lost, & do not stray too far from your intended route.
IF you feel that you have strayed too far from your intended route, OR you failed to tell anyone where you were going, then there are practicle things you can do to stay safe & perhaps find your own way out.
1) If you are low on water, find some if you can without straying too far from your present position. Low ground is generally better than high ground, though a rock plateau can often hold water in holes & basins in the rock. In flat terrain look for greenery growing. Usually this is trees or bushes. This could prove to be a water hole or a water course.
2) Remember that providing you keep yourself safe & have water, TIME is not an issue. Staying alive is more important than losing your job! Concentrate on staying alive & getting out, relax if you can & don’t panic.
3) You may need to construct a simple shelter from the sun or bad weather. With this goes making a fire, but make sure the fire is SAFE & can not spread! Clear an area of 5 paces all around your camp site, but only make fire if it is safe to do so. In extreme hot & dry conditions you should not light a fire.
4) During the day listen for the sounds of people; vehicle engines, car doors shutting, dogs barking, house doors closing, the sound of chainsaws or axes cutting wood or the sound of a generator or water pump. Look for smoke from camp fires or house chimneys. This will give you a direction to follow, but make sure you do NOT go round in circles. Line up three trees or land marks or a combination of these in the direction you need to go. When you get to the first marker, put your back against it & line up the remaining two markers with another third one. Continue on & repeat.
5) At night listen for the same sounds, but unless they are close-by, just mark the direction with rocks or sticks or mark trees & wait until daylight unless you have a torch or are fairly certain you are on safe ground. Travelling in the dark can be dangerous & you do NOT want to injure yourself. Look for vehicle headlights, radio tower lights, house lights, camp fires, lighthouse lights if you are near the coast. Watch for aircraft lights, there may be an airstrip not too far away.
Low ground can be good for finding water, but high ground will give you the best chance of seeing something that will help you get out. High ground will also make you more visible if you keep a fire going. Adding green vegetation to a fire will create more smoke. Passing aircraft may also spot your fire.
THREE is the S.O.S. signal, three whistle blasts, three gun shots, three fires (keep them safe), three COOEEs (a shout), three air horn blasts, three flashes from a torch at night, three flashes from a mirror during the day. You get the idea.
IF all else fails, going down hill SHOULD eventually lead you to a water course/source. EXAMPLE: you are on high ground, you go down. When you reach the lower ground, say a valley or gully, it too should go downward in one direction. Follow this downward & continue doing this until you find a water course. Mountain areas at their highest points produce what is called "Header Streams". These are where the water source starts from & these eventually run into streams or creeks which eventually lead to lakes & rivers. Water is also a source of food, & communities are usually built close to a water source.
If you do not expend too much energy, you can survive roughly 3 weeks on water alone, no food. But you can only survive roughly 3 days without water.