Start with vines and trailing vine-based plants. Add trees for height, and drape vines as though they are growing from them and trailing down the wet, dense bark. Don't back yourself into a wall thinking you need real trees. While potted trees and plants are a nice touch, with some creating lighting, you can use trees that are just short of cardboard. Vines and greenery can be plastic, silk or even crepe paper, depending on how realistic you need your scene to be. Add real or silk flowers -- colorful tropical flowers work best. Keep in mind that lighting and composition is key.
Establish the jungle very quickly by adding in a couple slithering snakes -- nothing says jungle likes snakes. Again, don't worry about the real thing; fake snakes can look very real, or if you're going for a more abstract look, try paper snakes.
Mist down the trees and animals -- as well as any people in your scene -- to create a hot, humid look.