This section is from the book "The Carpenters' Guide", by Harvey Miller. Also available from Amazon: The carpenters' guide.
To space the joists, measure and mark 15" and 17" from the corner on the sill and continue to space 16" from these markings, set the joists between these lines and they will be 16" on centers across the building.
If there are two rows of joists and you wish to lap them in the center, space one side 2" less in the first space so they will run parallel. (Fig. 8.) Where a sub floor is used, place a joist or header across the ends of the joists for a bearing of the sub floor. Also a partition of rooms having no sub floors; bearings, or headers, should be cut and nailed in between joists to support sub floors at all openings.
Locate chimney, cellar and all other openings and trim them the required size. Where the span of the joists are more than 12', cut a row of bridging and fasten them in place by nailing the top, leaving the bottom to be nailed after the sub floor is nailed in place. See that the crown of every joist is up. Where there is too much crown, straighten them so the top of all joists and bearings are level. (Fig. 8).
In nearly all buildings it is best to lay the sub floors diagonally, so the finished floor can be laid to suit the room. Measure equal distances from the corners on both walls and place a floor board across to those points, lay the sub floor from this board, and the floor will be diagonal or 45 degrees. Trim the projecting edges even with the outside of the joists and flush with all openings, nail all boards with two 8d nails in each joist, placing the nail 3/4" from the outer edge of the board. (See fig. 8.)