What I used for materials:
1 white canvas
black sharpie marker (fine & bold tip)
different shades of "blue" Craola crayons (about 10-15 crayons)
Now I will walking you through the step by step:
What you do need to remember is to start at the top of the canvas and have the different shades of blue drip down the canvas. Once you get enough wax dripped--to make it look like rain, put the canvas off to the side and let it dry/cool down. Once the canvas is ready remove the tape and you have something like the image below.