First settle on any princesses and ballerinas pictures that you love. Do you like Cinderella, Princess Ariel or any particular ballerina? Download princess and ballerina pictures off the internet. Look at picture books or story books with illustrations. You can utilize trace paper. Chose simple pictures without minute details; for instance, Princess Jasmine is pretty easy to actually sketch out without trace paper.
Your library is a treasure trove for princess as well as ballerina pictures. 'How to draw princesses and ballerinas' is also the name of an activity book whose author is Fiona Watt.