Leaves take the leading role when shooting foliage, but think also about the tree's branches and trunk. The angle when looking down on the roots from eye level is also good, but shooting low-angle shots (from a low position) while boldly looking up through a wide-angle lens can emphasize the tree's strength.
In talking about fall foliage, it's easy to generalize, but in truth there is a lot of color variation between different trees and even among individual leaves. Try taking pictures of green, yellowish green, and yellow colors or even the colors as they change to red. Capturing such beautiful gradations makes for pictures you'll never get tired of looking at.
Try paying attention to individual leaves. Even if foliage looks beautiful in large volumes, it is surprising how few leaves actually have nice colors or shapes. Finding the ones that do and shooting them, however, is fun. To get leaves to overlap, if you aim for them with a standard to telephoto lens, it is easier to shoot them in such a way that the gaps between them become less noticeable.
When the fall foliage is at its most colorful peak is not the only time to shoot, though. Fallen leaves are also quite photogenic. There is beauty in the figure of a leaf after it has completed its purpose and before it begins to decay. Especially just after a rain, wet leaves look particularly beautiful. Try looking down while you are walking. Something you would not normally notice is almost sure to catch your eye.