Instructions
Become an anime/video game/manga enthusiast. In order to participate in crossplay, you must know which character you want to portray, and that character's relationship to other characters the other players may assume.
Get involved in the crossplay community by finding others who enjoy it. While you might think that showing up to your first crossplay event without having done much research would be no problem (and you may be right), it is more fun to immerse yourself in the crossplay community first.
Dress up as a favorite character. Try to remember that you need to make your costume yourself while designing it. Don't get carried away. If you get it wrong, it won't go unnoticed.
Design your costume and set to work making it. Dress up and head for the crossplay convention.