Formal:
* À demain, mon ami/mamie. (This is the most common and polite way to say it.)
Informal:
* On se voit demain, mon pote/ma pote. (This is more casual and is used with close friends.)
* À plus tard, mon pote/ma pote. (This means "see you later" and can be used for tomorrow as well.)
You can also say:
* On se retrouve demain, mon ami/mamie. (This means "we'll meet again tomorrow.")
Remember:
* Ami is for male friends, amie is for female friends.
* Pote is a slang word for friend, so it's more casual.
* Mamie is a more affectionate way to say "friend" and is often used for a female friend.
Choose the phrase that best suits the context and your relationship with the person you're talking to.