What are the three main rules in Harry Potter series?

1. Never talk about magic in front of Muggles. This is one of the most important rules in the Harry Potter series, as it helps to keep the wizarding world a secret from the non-magical world.

2. Never use magic on a Muggle. This rule is similar to the first rule, and it helps to protect Muggles from being harmed by magic.

3. Never do anything that could bring danger to the wizarding world. This is a broad rule that covers a lot of different things, but it basically means that wizards and witches should always be careful not to do anything that could jeopardize the secrecy of the wizarding world or put any of its inhabitants in danger.