One of the easiest ways to make your photographs stand strong is to combine horizontal and vertical lines together.
Since the human eye is naturally trained to follow the direction of lines, why not incorporate this into your imagery? Many of the elements in our environment are vertical. Thus, when we incorporate them into our images, we should utilise these features.
There is no right or wrong on this issue: These are just ideas based on my experience:
Where one man is standing tall, ensure you find a way to capture this appropriately. It might mean capturing his silhouette, or shooting from a lower angle against a single-coloured background (like a blue sky or stark wall).
From the sapling to the forest, trees grow vertical mostly. Yes, their branches shoot off at all angles. So the trick is to use the light to capture the trunk of a tree and display that element effectively. Depth-of-field and under or over exposure can be most effective in this style of photography.
There is no other subject that stands more vertical than the standard building. From the LEGO™-Mansion through to Eiffel Tower, it is their sharp and straight edges that make them the most formidable subject to capture in vertical. Whilst a building can look very art-nouveau when photographed at a 33-45degree angle, it will look its best when the walls are vertical.
Capturing vertical subjects so they appear to burst out of the photograph is going to capture your viewer instantly. This will mean that whilst the verticals remain straight and true, they will bend at either the top of bottom as they leave the frame.