You need:

light green paint

First:  Paint your wall with the paint roller using

a medium green. Thin the paint with a little water,

but don't make it too thin. Don't worry about

getting this layer smooth and even. You can roll

the paint on in all different directions.

Second:  Thin some dark green paint with a little

bit of water.  Don't make it too thin, though.  Dab

it on your green wall.  Take a rag and smear it.  

You want to make the background splotchy

looking with several shades of green.

Third:  Thin the dark green paint with water.  

Not too thin.  Take your skinny brush and paint

leafy, palm tree shapes like this on the background

you painted.  

Fourth:  Take the light green paint, thin it with

a little water and paint the same shaped leaves

as you did with the dark green paint.  It is okay if

they overlap or are on top of the dark green leaves.

Fifth:  Shade and highlight the light colored leaves to

make them look more realistic.  Don't worry about the

dark green leaves, they are supposed to be part of the

background.   Paint in skinny lines with the black paint

and then smear them a little with a rag.

Last:  dab on some tiny patches of white paint on

the tops of the leaves to look like little patches of sunlight

filtering down through the leaves.  

Now your Jungle Wall is finished!