He told me i should... but how?

My guy friend and i were talking the other day, and i was feeling sad. He asked why and i told him that "I thought nobody liked me," because i dont think i am all that pretty or anything, and i tend to submerge myself in my school work... So anyways, he told me that "I know a bunch of people that like you, but they are too shy to do anything about it. You need to flirt and believe in yourself!" So, i am trying to take his advice and "Flirt more" and "believe i am pretty" but i dont know how... so, my question is how do i flirt more, any tips? Also, tips on confidence? Thanks.