Subfloor should be dry, clean , and level. Do a moisture test on the subfloor using the calcium chloride method and/or a moisture meter. Resolve any problems before proceeding. If the concrete is new, then allow at least 30 days time for drying. You may also apply a sealant to the floor. If your subfloor is concrete, place a moisture barrier on the concrete.
Next, install plywood, usually CDX grade in 4’ by 8’ pieces. When installing the flooring, allow space between walls and flooring for expansion space. The first row should be top and blind nailed. For the other rows, nail tongue at 45 degree angle. A pneumatic naileris the recommended tool. Make sure to stagger the joints from row to row. You do not want to see many end joints lining together on adjacent rows.