How to draw when you "think you can't draw": 1. Trace a picture. This will help you get a feel for shapes & scale, and help you develop muscle memory. (For practice only - don't infringe copyright!) 2. Use stencils - they're a great way to jumpstart doodling and drawing!
3. Draw simple shapes and expand from there. A circle, with a ray of ovals around it, becomes a flower. Add a line below the petals and you've got a stem. Add ellipses to the sides of the line, and now you've got leaves. Everything starts with lines and shapes!