Start by getting your ideas together. Look at inspiration and reference photos if you need them, draw little thumbnail sketches to get an idea on composition and perspective. I usually doodle an idea 2 or 3 times before sitting down and making it a project.
Next, start lightly on the type of paper that suits your needs. As you develop it on paper, add on the details and give things more shape, depth, and emphasis.
Work for as long as you'd like, as Leonardo da Vinci once said "Art is never finished, only abandoned" and once you feel satisfied, you stop.
Don't be afraid to make marks on paper, if you don't like it, you can erase, start over, or make it work (I love happy accidents).
Just keep in mind that you won't be the best artist overnight, but just because someone can draw a ballerina super realistically, it doesn't give them anymore of a right to make a mark on paper than you.