Consider how photographs will be used or displayed.  Will prints be made, or will the images simply be displayed on a computer or television?  For prints, I recommend shooting in portrait (long side of the image vertical) or landscape (long side of the image horizontal) position, based on the subject, to allow for the largest good-quality-print possible, but for display only on a computer or TV, I recommend that all photographs be taken in a landscape position as this will allow for the best use of the screen space.  I also suggest shooting multiple images (if possible) with the appropriate camera orientation if both prints and computer/TV display are desired.