Consent is the whole rulebook
Every uncomfortable anonymous-chat story starts with someone ignoring a signal. Short replies, topic changes and long gaps are all answers. Ask before steering a conversation somewhere personal, and accept 'no' the first time without negotiating.
Pace and volume
Do not send eight messages before the other person has sent one. Rapid-fire messaging reads as pressure even when it is enthusiasm. One thought per message, then wait.
Humour without collateral damage
Anonymous rooms run on jokes, and the funniest ones are not aimed at a person's identity. Punching at groups gets rooms shut down and drives out exactly the people who made them interesting.
Handling bad actors
Do not feed trolls, do not screenshot-and-share private conversations for points, and do not organise pile-ons. Block, report, move on. A community's health is mostly the sum of small, boring decisions like that one.
Be someone worth replying to
Answer questions you are asked. Remember one thing from earlier in the chat. Say when you are leaving. That is roughly the entire difference between people who find good conversations online and people who conclude that nobody talks to them.