Whichever direction you choose to do it, hanging drywall can be somewhat time consuming. Some people insist that hanging drywall horizontally is the right way to do it, while others say hanging it vertically is easier, especially for non-professionals. The main reason for hanging it horizontally, say some people, is that it ultimately leaves you with fewer joints to tape and mud. There is also the issue of fitting the drywall within a given area. Since drywall typically comes in 4 foot wide sheets of varying length, a wall that is 8 feet from top to bottom will require 2 sheets, one on top of the other with no cutting, except from the sides. However you decide to hang it, you should choose the method that works best in your opinion.
Hanging Drywall Horizontally
As stated, drywall comes in 4 foot widths, often in 8 foot lengths, but it comes in 12 foot lengths as well. The distance from floor to ceiling in the average residential home is 8 feet. Hanging drywall horizontally, then, allows for a perfect fit with one sheet on top of the other. No horizontally-made cuts are necessary (assuming the wall has no odd shapes or fixtures). Imagine a wall that is 8 feet top to bottom and 16 feet side to side with no fixtures. In this case, 4 full sheets of drywall hung horizontally would fill the entire wall. You would be left one long bevel joint of 16 feet, and one butt joint of 8 feet to tape and mud, not counting the corners. That's a total of 24 feet of taping and mudding. Covering the same wall with vertically placed drywall would also be accomplished with 4 full 4-by-8-foot sheets: placed vertically side by side. This would leave you with the same total distance to tape and mud: 3 bevel joints of 8 feet each.
Hanging Drywall Vertically
In the previous example, there doesn't seem to be any benefit from hanging the drywall horizontally. In fact, it may be more difficult for the amateur. Butt joints (drywall joined end to end) seem to give non-professionals more problems than bevel joints (side to side joints), because bevel joints create a narrow groove that absorbs the mud. Butt joints require more finesse when mudding. On the other hand, affixing the drywall to the studs with screws may be easier when it's hung horizontally. The bottom sheet is only 4 feet off the ground, making it easy to reach. Hanging it vertically, you must climb a step stool to reach the top corners.
Depending on who you talk to, you may receive conflicting opinions about the proper hanging of drywall. Some will swear that hanging it horizontally is by far the easiest and standard way of doing it, while others will argue that vertical hanging is better. Try it both ways and decide for yourself which direction is easier. If hanging drywall is not your profession but a one-time do-it-yourself project, and you find hanging it vertically to be easier, by all means do it. Ultimately, the right way is going to be the way that works for you.