Eliminate any problem spots to make the subfloor level. Sand minor humps down with a hand-held or orbital sander to make the subfloor level. To fill any dips or low spots, use a leveling compound (also known as floor patch). Mix up the compound according to package directions, fill in the dips, then pull your straight piece of lumber back and forth over the spot to flatten and level it with the rest of the subfloor.[7] Denver Hardwood Floors

Tongue-and-groove: One side and one end of the plank have a groove, the other side and end have a tongue (protruding wood along an edge's center). The tongue and groove fit snugly together, thus joining or aligning the planks, and are not visible once joined. Tongue-and-groove flooring can be installed by glue-down (both engineered and solid), floating (mostly engineered only), or nail-down (not recommended for most engineered).

If your floors are in need of a deeper cleaning, use a wood floor cleaner. Follow the instructions for diluting the cleaner in water. Clean the floors with a damp mop, going with the grain. Then, go back over the floor with a clean, damp mop to remove any excess cleaner. Finish by drying the floor completely with a dry towel. Remember, leftover standing water could damage your wood floors. Denver Hardwood Floors
Another common hardwood floor malady is the development of gaps between planks. The most common causes of gaps between the boards is Mother Nature. Wood shrinks as it dries out, and it expands when it gets wet and humid. That regular expansion and contraction over time is the most common cause of gaps, and is the main reason why most gaps are seasonal in nature. Perhaps your best plan of action is to exercise patience. Denver Hardwood Floors
Most floors use a tongue-and-groove design for connecting adjacent strips. This design makes replacing a single strip or plank challenging, but not impossible. First, look for any nails in the damaged board and drive them as far through the board as possible by using a hammer and nail set. Carpenters use nail sets to drive nails flush with trim without damaging the trim with a hammer. After you’ve cleared the nails, it’s time to remove the damaged board and install a new one. Follow these steps: Hardwood Floors