Secure the boards to the sub floor by secret nailing into the tongue of the board at a 45-degree angle, or glue the wood to the sub floor with professional wood flooring adhesive such as the Sikabond range of wood flooring glues.
For a floated wood floor each wooden floorboard is secured to the next one, not the sub floor. Use PVA wood glue on the T&G joint only and lay it onto a suitable wood flooring underlay
Where necessary use straps and pull bars to pull the boards together and hold them in position until fastened by nails or a cured adhesive.