Vertical lines have the ability to convey a variety of different moods in a photograph ranging from power and strength (think of skyscrapers) to growth (think of trees).
As horizontal lines can be accentuated by shooting in horizontal format vertical lines can be used very effectively by swapping the way you hold your camera into a vertical framing. This lengthens the vertical subject further which can emphasize it’s height.
The other option is to break this rule and frame your vertical subject horizontally which will give it the sense that your image can’t contain it (quite effective if the vertical lines are very strong).
Once again it’s important to attempt to keep your vertical lines as much in line with the sides of your image as possible. This is not always possible if you’re shooting looking up an image as the subject will taper off towards the top – but attempt to keep its center as straight as possible and you should be ok.
Keep in mind the rule of thirds when you have strong vertical lines in a photograph. Placing a line directly in the middle of a shot will effectively cut your image in half. This can be used with dramatic impact but also can leave your image looking segmented.
Keep an eye out for vertical lines that are repeated in patterns in your images as they can be used to great impact – particularly if they are contrasted with other shapes and lines going in different directions.