The stereotyping checklist
It can be tough to keep conscious track of when you're stereotyping. So if you genuinely want to not stereotype and are looking for a shortcut, just remember this: If you are treating someone differently because of something they didn't choose, then you're stereotyping, don't do it.
Example: If you react differently to someone who's overweight, you're stereotyping, don't do it. Also if you react differently to someone you find massively attractive, that too is stereotyping. Be normal, be usual.
Example: If you treat someone differently because of their gender or name or caste or religion or appearance or language or food choices, you're stereotyping, don't do it, none of these started out by their own choice.
All the best!