Clean it well with a wet dry vacuum.
How to level floors for hardwood installation.
Floors are rarely perfectly level.
Remove any obstacles from the floor.
Then using a floor leveling compound or asphalt shingles shim the dips so the floor is level.
How to level a floor for installing hardwood before you install hardwood flooring follow the directions above for fixing high and low spots in a wood or concrete subfloor.
If the area is very large use a long straight 2 in 4 in 5 1 cm 10 2 cm board and set your level on top of it.
Hardwood floor installation can be slowed by an uneven subfloor.
A plywood subfloor will bridge any minor waves in the existing floor and leveling compound would help too.
Make sure you apply a cementitious flooring leveler you can nail through later.
You will have to make sure your joists can handle the addition of considerably more weight from the plywood subfloor and any floor coverings.
Pound nails into the subfloor with a hammer and set screws slightly below the surface of the subfloor with a screwdriver.