Many factors determine the overall look of a wood floor, including the species of wood, the quality of its grain and finish, the size and consistency of the individual courses -- and possibly the most noticeable, the direction or pattern of the layout. There are different reasons for running the wood courses in different directions, depending on how much of the floor is to be covered, so exercise careful design consideration before beginning work on any floor.
The Cross-Joist Standard
The first consideration is always whether or not it's feasible to adhere to the construction standard of running all flooring courses perpendicular to the direction of the floor joists. This is done not only to provide solid places to nail into every time the board crosses a joist, but also because if the subflooring warps or sags slightly over time, boards running the same direction as the joists may separate slightly at the seams, causing the joints to open up and create visible gaps. If the boards run across the joists, this will not happen -- they will simply "bridge" over the sag, remaining flat.
This practice is an especially good idea if the construction is of an older style in which subflooring wasn't laid out in sheets of plywood, but rather courses of 3/4-inch-thick "shiplap" boards were run perpendicular across the joists. The bottom line is -- if you attempt any other direction, place cross-bracing in between joists at about 8-foot intervals. This will help cut out any movement that may cause gaps or creaking noises down the road.
Courses are then laid out starting with the groove side of a "tongue and groove" flooring board tight against the desired leading wall, and then each consecutive course is tapped tightly into the tongue side and fastened into the subflooring through the tongue -- at an angle -- as described in the National Wood Flooring Association's "Wood Flooring Installation Guidelines and Methods" handbook.
The Issue of Aesthetics
As with nearly all aesthetic considerations when you're remodeling, much depends on the scope of the job. If the flooring is only being laid in a smaller room adjoining a large run of open space or a hallway that has a different look, then the best look, for continuity's sake, is to separate the room from the hall with a threshold, and continue with the courses perpendicular to the direction of entry. That being said, if the room is particularly long in one direction, but not the other, then the courses usually look best going lengthwise with the room to avoid the pattern looking too cut up, or busy. In cases of whole-level flooring jobs, it's customary to run the flooring away from the main entryway -- in the direction of travel -- then spill into each adjoining room and corridor accordingly. This tends to capture the eye and pull the attention immediately out into the open space of the home, making the area look much larger and more open.
In any case, there are nearly limitless ways to lay flooring, depending wholly on personal preference. Any number of patterns may be adopted using shorter boards -- such as cross-hatching diagonal runs, or closing geometric patterns of squares or rectangles. You can even border part or all of an area with one or more courses, and then fill in the space within the border with either standard runs or smaller patterns, giving the room an almost "tiled" look. The length of the individual boards and where they leave off may be arranged either randomly or in a specific pattern for different looks. The best thing to do is weigh all of these factors, and then sketch a few different ideas to scale on paper, noting the dimensions of the room, as well as its intended use and furniture placement.