Look for seasoned wood, or wood that has been aged for six months to one year. If you are buying firewood in advance -- for the following year's winter season -- it may be green. Stack and store green wood in a sunny location for at least six months.
Choose wood that is lightweight, indicating that it is fully dry. Strike the wood against an object, and listen to the sound. Dry wood emits a "sharp" sound when it strikes something. Wet wood makes a "dull" noise.
Obtain firewood that is cut to fit in your fireplace or woodstove. Cut or split it to size if it is too large.
Select pieces of firewood based on your needs. Thin sticks ignite quickly, and burn even more quickly. Thick logs start more slowly, but burn for much longer.
Avoid pine wood covered with tree sap. This sap is very flammable, and might cause a chimney fire. Avoid wood that is -- or has been -- covered with poison ivy. The fumes from the ivy-covered log can cause a reaction in some people.