The First Course of Flooring
Some floor installers prefer to lay the first course against a prominent wall for two reasons: it makes the installation easier, and the lines made by the boards are more likely to match the line of the wall. In a square or rectangular room, even a slight difference between them can be noticeable.
In some installations, however, such as when the room has an irregular shape or the flooring is diagonal to the walls, starting against a wall isn't practical. In such installations, it's better to snap a line down the middle of the room as a reference for the first course.
Why Lay First Course in the Middle
Flooring expert Kim Wahlgreen in Hardwood Floors Magazine advises that beginning in the middle distributes the expansion of the wood in two directions and is always a good idea. It may reduce the possibility of cupping.
It is especially advisable to start laying flooring in the middle if a room if it is large and the doorway is centered in the wall, because it's easier to guarantee a straight sightline from the door. Moreover, if you are extending a floor from a living room into an adjoining hallway, and you want the first course to run along the hallway wall, you must run it down the center of the living room.
Measuring the Line
Visual acuity requires the sight-line of the floor to extend straight out from the vantage point from which people are most likely to view it, whether it's the entry door, a hallway or a prominent feature. After making a mark at that point, make another at the opposite side of the room, using the walls as a reference, and snap a chalk line between the two points.
It isn't necessarily important for the line to divide the room in half or even to be parallel to a wall, but its placement should produce some kind of visual symmetry.
Most installers face-nail or glue the first two courses to the sub-floor. Gluing adds time to the installation, but by using glue, they avoid visible nails in the middle of the finished floor.
The second course must have the tongue facing away from the first course, so installers cut splines that fit into the groove of the first course to act as makeshift tongues. After installing the first two courses, it is possible to nail off the rest of the flooring with a flooring nailer, working first toward one wall and then toward the other.