Choose a good strong visual point to be seen from. Any fire you build, must be in a clear location to ensure passing crafts stand the best chance of spotting you.
In a clearing or on a hilltop, make three signal fires, place them in a triangular pattern (a known signal for help). Space them about 50ft. apart so that the pattern can be distinguished from overhead.
You want the smoke from your signal fire to show up against your background area. In snowy conditions for example you will want dark smoke (black). You can make dark smoke by burning the tires on your car, your vehicles oil, even plastics may work. In a forest you would want white smoke. You can get this by burning dry leaves and or green boughs. For ample smoke, use green and wet wood on top of your burning fire.