It takes practice. You will start out as really bad. Don't pain the streets in this stage cuz you'll just embarrass yourself. Find a panel your legally allowed to paint, and preferably where nobody can see and just practice. Paint a piece, take a picture.
Keep drawing on paper too. Pencils and paper, and lots of sharpies.
I tried too, and didn't make it. My friend and I started together, he make it I didn't.