#1 Make sure you address the person who the email is for appropriately.
"Hey" is informal and should be used for people you have a personal relationship with. "Hello _________" or "Dear __________" is more appropriate for teachers, counselors, or other adults you are emailing.
#2 Use complete sentences and check your spelling. You want to make sure your message is clear and understandable.
#3 Don't forget your manners. Remember to say "please" if you are asking for something. Also, it's always nice to end your emails with a "Thank You".
It never hurts to be extra respectful, nice, or courteous in emails. Putting your best food forward always has its benefits!