How to build a campfire anywhere. A fire needs 3 things: fuel, air, and heat. A good small fire will grow, but too much air will dissipate the heat, and too much fuel can smother the fire. To get a terrific fire, you need fuel of the right size, with enough air circulating around it, and concentrated heat to get it burning well.
What’s the right size of fuel? Well, it is easy to light a match with another match. You might even be able to light a stick that is twice the size of the match, but not much larger. So you need a mix of wood from match size, up to the size of the wood you eventually want to burn. Bark is harder to light than wood, so even if the wood is of a useful size, you may want to split or peel it with a knife or ax. Wet or damp wood is hard to burn, though it can often be used once the fire is established.
How much air? A good rule of thumb is to use roughly half as much space between sticks, as the diameter of the sticks. That gives enough room for air to circulate freely, while concentrating the heat between the sticks. As the fire gets established, you may want to reduce that a bit, and for larger logs (4” or more), they should usually be right next to each other to make good coals.
Heat rises, so you need to progress from smaller fuel at the bottom, towards larger, longer-lasting fuel near the top. As a practical matter, it is easier to hold back the largest fuel and add it after a small fire is already burning well. If you are worried about getting a fire started in bad weather, carry a firestarter, like cotton dipped in wax, petroleum, or bacon grease, a little fatwood (dry pine with lots of sap, available in many home centers), or a small bit of candle.