To build a fire, it helps to understand the basic principles of a fire. Fuel (in a nongaseous state) does not burn directly. When you apply heat to a fuel, it produces a gas. This gas, combined with oxygen in the air, burns.
Understanding the concept of the fire triangle is very important in correctly constructing and maintaining a fire. The three sides of the triangle represent air, heat and fuel. If you remove any of these, the fire will go out. The correct ratio of these components is very important for a fire to burn at its greatest capability. The only way to learn this ratio is to practice.
You will have to decide what site and arrangement to use. Before building a fire consider the area, materials and tools, time available, and the purpose of the fire. Is this fire mainly for cooking, or do you plan to use it only for a source of heat?
Next, look for a dry spot to build your fire. Make sure this location is protected from the wind, and is placed near any shelter you may build. Think about where you want the heat concentrated at your campsite. Before building, make sure there is enough wood or other fuel to sustain whatever type of fire you choose.
If you are in a wooded or brush-covered area, clear the brush and scrape the surface soil from the spot you have selected. Clear a circle at least 1 meter in diameter so there is little chance of the fire spreading.
If time allows, construct a fire wall using logs or rocks. This wall will help to reflector direct the heat where you want it. It will also reduce flying sparks and cut down on the amount of wind blowing into the fire. However, you will need enough wind to keep the fire burning.
Caution: Do not use wet or porous rocks as they may explode when heated.
In some situations, you may find that an underground fireplace will best meet your needs. It conceals the fire and serves well for cooking food. To make an underground fireplace or “Dakota fire hole.” First, dig a hole in the ground with sloping sides around 45 degrees but deep enough to shield all of the fuel. On the upwind side of this hole, poke or dig a large connecting hole for ventilation. Build your fire in the hole but be mindful that with reduced ventilation the fuel needs to be more loosely layered.
If you are in a snow-covered area, use green logs to make a dry base for your fire. Trees with wrist-sized trunks are easily broken in extreme cold. Cut or break several green logs and lay them side by side on top of the snow. Add one or two more layers. Place the top layer of logs opposite those below it.
Information courtesy of the U.S. Army Survival Manual