My advice for a beginner cosplayer would be to just be yourself.
For most people, cosplay is a way to escape reality.
Just because you cosplay a certain character does not mean you have to act like that character.
When I cosplay I'm not worried about being too into character, I'm mostly in it to have fun. Which leads into my second piece of advice, have fun. Always have fun when you are doing anything, whether it is for cosplay or not.
Having fun, to me, is one of the more important parts of cosplaying.