Inside the forest, one must focus on vertical compositions by holding the camera at ninety degrees to the normal position along with a sense of depth and it can make look trees taller and more dramatic.
Try to reframe each horizontal landscape shot by rotating the camera with a vertical portrait composition to explore the possibilities. For forest photography, choose a bright overcast day since the diffused light harsh shadows and burned out highlights. Also, chose the golden hours for some good light when the light is horizontal.
If you have the harsh light use a circular polarizer and keep on repositioning it to get appropriate amount of light entering the lens. With the use of the polarizer, add up to 1 or 2 stops of shutter speed. For good compositions, look for patterns, diagonal lines, and curves. In forests, curves are more interesting than straight lines like a bend in the river, a pathway or a weirdly shaped tree. Pan and move around carefully to compose the picture since one small step can make a big difference to the image.