eBird has two bird tutorials to help you learn how to estimate numbers:
Counting Birds 101, http://ebird.org/content/ebird/news/counting-101/
Counting Birds 201, http://ebird.org/content/ebird/news/counting-201/
David Sibley’s website has several practice quizzes to help you learn how to estimate numbers of birds in flight or in a flock. See http://www.sibleyguides.com/quizzes/
