Do you want to cosplay a character specifically from a manga, anime, video game, cartoon, movie ? What specific genres/anime/games etc. do you like ? Are you going to buy it online, closet cosplay, or are you going to make it yourself ? If you're making it, what is your skill level ? Are you willing to wear wigs/contacts/dye your hair ?
It is so much easier for us to narrow it down, so we know what to look for so that. It's difficult enough to give suggestions to a stranger on the internet, so answering those questions will certainly help.