Draw a few slanted parallel lines for falling rain
Vary the length and spacing of the lines
Add clouds above the rain
Draw a wet ground or puddles below
Include raindrops hitting surfaces with small splash marks
Use lighter lines in the distance and darker lines in the foreground
Add wind direction by tilting the rain lines slightly
Shade the sky darker to suggest a storm
Draw umbrellas, trees, or buildings for context
Add reflections in puddles for a rainy scene