as an example: my horses know when they can itch their head on me. i put my hand out and allow them to rub. they are NOT allowed to just itch their head on me when they have an itch, it's only allowed when i offer a scratch.another example: they are NOT allowed to beg for treats. they are only allowed to take a treat if it is offered to them. begging like that for food can turn into fingers getting bit off quickly.
any pushy or dangerous behaviors. most people think it's cute when a horse is "cuddly" but it is disrespectful. there's a time and a place for a horse to be cuddly and it's when you say they can. it is disrespectful for them to walk into your space when they please, it is YOUR decision when they can be in your space. turning their butt to you in any circumstance is very. very, very disrespectful and dangerous.
I second what Eliza said! That drives me crazy! Rearing, striking, biting, kicking, or any kind of dangerous behavior is a no-go. Also pawing excessively & getting greedy/rude about feeding time or treats. General respecting your personal space and your authority as the herd boss are the most important to establish for a youngster. Good luck with your horse!