Use your field guide to setup you lay out. Because this is just an animation test, you don't need a spectacular BG just a well composed and staged space to allow you leaf to move about and not get lost in the background details. BG is one layer and in this case just one held frame.
To make animating a little easier, plot out your arc path. Below is a very simple path from branch to ground. Notice how the action has been staged so the motion is readable throughout the piece. Enough of the ground plane has been left open for action. Do not allow your leaf to sit, land, or touch the bottom edge of the frame.
Next, using the arc path you just drew, tick off points where you think the leave will appear on the arcs. The closer together the drawings, the slower the action, while faster action requires more spacing between drawings. As gravity pulls the leaf, it slices through the air moving quickly. Denser air or wind or other factors will slow the leaf causing it to change direction-more drawings here. Once gravity takes over again and the leaf again slices through the air it will pick up speed and slow at another change of direction etc. When landing the leaf moves the slowest and finally slows out to a stop. Lots of drawings here.Now you're ready to test it. I think you will find that the randomness of the tick marks will be corrected when you test your work and the path begins to feel right.Most of the arcs will be created by air current and position of stem. Remember also that the fresher a leaf is the more pliable it is. Meaning that it it will bend and roll as it moves along it's path to the ground. The more dry a leaf, the less flexible it is. But this is all relative, if the leaf doesn't bend or roll it will look really stiff on it's way down. Larger leaves 'float' better while smaller/thinner leaves tend to 'tumble'. What kind of leaf are you using? Have fun animating!