I am going to be making a cliff in Hawaii using an avenue, however I have no clue where to start. Does anyone have any suggestions?

Sounds beautiful & fun to create! When I build something up like that, I start with a focal point...like a pond or waterfalls, then start adding in trees like palm trees for yours, tropical flowers & rocks, boulders, grass mounds. There's some cool boulders & rocks in the YoDepot. I also like to add an extra touch in of sun rays, crashing waves and even those old colorful fireflies (YoDepot). Good luck and can't wait to see the finished project!