Your choice of lumber depends on what you plan to use it for. The Department of Commerce has set specific standards for grading lumber. Most of the lumber you find in lumber yards will be softwood--probably pine, fir, cedar, or redwood. For general construction projects, structural or number one lumber and common number-one or -two boards are sufficient. If appearance is important, look for select boards graded 'B' for better quality. Grades 'C,' 'D,' Finish and Prime get successively better in quality as well as price. Lumber will be stamped to identify the grading agency, mill identification, grade, species of wood, and seasoning or moisture content. Hardwoods are generally used for furniture, cabinets, or floors and may have to be special ordered. They are graded by the National Hardwood Lumber Association. Look for the letters F-A-S, which stand for Firsts And Seconds, if you want top quality. Paneling has still another set of grades, depending on its use. The best, graded A-A, will have highly finished surfaces on both sides. It's commonly used for built-in cabinets or fences. When only one side will be visible, such as paneling, look for a grading of A-D. Other plywood grades are for specialty uses like subfloors, sheathing, or marine purposes.