Style plays the biggest role in it, if you already have a few alt girls added on ig/tiktok check their likes and reposts and if you see alt boys just copy their entire style including clothes, hair and everything
For physique and characteristics, you want to be lean as possible, either be tall and skinny or short and hella jacked
Keep in mind that most of them wear a shit ton of makeup so go for ones somewhat above your looks and not for a looksmatch
Piercings and new rocks are also good to have, new rocks also boost your height so free frauding