The type of wood you can make all the difference. Hardwoods like maple, oak, ash, and beech burn hotter and cleaner and won't damage your oven. Your hardwood also needs to be seasoned and dry. Wet wood will produce a lot of smoke. Don't use resinous woods like pine or fir trees. The sap in pine trees will smoke, give your pizza a bad taste, and ruin your oven. Moldy, rotten, or wood with fungus on it will affect the taste of your food and could be dangerous to use. Also, avoid treated or painted wood as the chemicals could also be harmful to you and your oven. Treehugger.com has a really nice article on North American Hardwoods and how to identify them.