A question I get a lot from photographers is, "When is an appropriate time to shoot vertical and when is an appropriate time to shoot horizontal?" The thing about landscape versus portrait photography is it's really again about a matter of preference. However, there are certain things that will work much better as vertical images and there's certain things that are obviously going to work better as horizontal.
Photos like basketball generally tend to be very vertical and thus you want to shoot them vertical. That's not to say all the time. Something like this, gymnastics, this works a lot better as a horizontal photo. Same with baseball. He's sliding into the bag, and a good rule of thumb is if it is a motion photo as these all are, you kind of want to play off of the motion that they are going. He's sliding right to left whereas the basketball player is coming up. So you want to kind of go with the direction of that motion when decided how to crop your photos.
Another nice thing about switching the orientation of your camera from portrait to landscape or landscape to portrait is it will totally change up your composition, and it just gives you more to work with. So if you're our photographing and no compositions are striking you, maybe the answer is turning your camera a different way and seeing how it works that way.
I generally tend to shoot most things horizontal. Simply based on the fact that I think the human eye can better understand, and it translates better to the human eye because we see horizontally. That's not always the case, but in my opinion I think nine times out of ten it is.
Again though, some people shoot only vertical. Some people shoot only horizontal. It's really a matter of preference.
If you do find that you're really enjoying shooting vertical images, I would highly recommend getting one of these guys. Which is a vertical battery grip. What's really nice about this is that it puts a second shutter here, in addition to the one here. So you can really comfortably hold it vertical and shoot. Great for sports. Great for portraits. Great for studio work. Again, it's up to you, vertical versus horizontal, but think about your subject matter. Think about what's going to make the most sense and think about what you like the best.
That's the basics of vertical versus horizontal photography.