A Discord server, despite being online, is still a public place full of people of all backgrounds. As such, you should always behave respectfully in any Discord server. However, any server should have a rules channel. These guidelines can help dictate how you should behave in that server. If you ignore the rules, don’t be surprised if you get muted, kicked, or banned from the server. Server owners and moderators can kick or ban members whenever they feel that the rules are being broken.
It’s safe to say that you should not be rude to people, pick fights, spam chat, or self-promote. Use some common sense to decide what is an is not appropriate. Also, be sure to abide by Discord’s own terms of service, or you may find your account in trouble with Discord itself.