When starting a fire, there are a certain order to follow to ensure that the fire actually starts and spreads to a heat level that is suitable for cooking.

Preparation

What is important to ensure before starting the fire is to collect sufficient material to get it going, till close to the end. The last thing that you want to be doing is to be starting a fire and just as its getting up, you run out of material to sustain and grow it. So its important to estimate correctly and collect the right amount of material beforehand.

Tinder

All fires are easiest started with tinder. Tinder could be anything that is flammable. In nature, tinder could come in the form of leaves, wood shavings or dry bark. The tinder is the most important part to creating a fire. If you can start your tinder going, most likely you would be able to progress to the other levels. It is also the most difficult part to get a fire going.

Middle wood

Once you have a flame going, you want next to bring it up to a bigger level, so it can eventually burn large pieces of wood which will produce the heat to cook your food. To bring up the flames, put in small branches and twigs in-between flammable material such as leaves. In the beginning you would need to put less wood and more leaves, but as the fire builds, you would slowly reduce the amount of leaves, till you realise that you don't need anymore to bring up the flames.

Large Wood

Depending on what you have off hand, the final steps to get a fire for cooking is to put in large branches or even logs. These material will burn easily enough if you have done the first 2 steps correctly. Once they burn, you can consider your fire to be self-sustaining and you don't need to be too worried about it going out too easily.