The first answer is, if you have solid hardwood, the wood has to be run in a particular direction. The hardwood should run perpendicular across the floor joists for more strength of the floor going over it. Not doing this can cause sagging of the hardwood and board separation.
If you are using engineered hardwood, you have the following choices below.
The second answer is personal preference; however below are some helpful guidelines to keep in mind. Often, it depends on what look you are trying to achieve.
The easiest way to make a decision is to look at the areas receiving hardwood and if there is a narrow hallway involved, then run the hardwood the long length of the hallway.
If you have hardwood in one large size room only, the direction is truly personal preference. The room will appear longer if the wood is run from one end of the room to the other.
If hardwood is in more than one room, but the rooms are open to each other, running the hardwood from the long end to the other end rather than from the front of the room to the back of the room will make the 2 areas seem larger.
Otherwise, the hallway will look chopped up.
Hardwood can also be installed diagonally or with a pattern such as a herringbone.