I've seen a lot of posts out there around how authors should behave before they've signed with an agent or a publisher, but there's no much around after you've signed, with the exception of the whole DON'T RESPOND TO NEGATIVE REVIEWS.
So here's some pointers on what you need to do once you've signed.
Know your industry: Understand how publishing works, be informed and know your role in this. (You should have done this already, but if you haven't then catch up).
Know when to announce: Whether you've sign with an agent or a publisher ,it's not okay for you to announce it until you're told you can. This is especially the case for publishers as a lot of them will want the first announcement to be on Publishers Market.
Understand editors have a job to do: They're not trying to destroy your literary baby. It takes a village to publish a book. Editors are there because of their experience and knowledge. They can see things that are needed that you can't and will also consider commercial factors that you've never even thought of. Work with them, not against them.
Respect social media site guidelines: Goodreads has Guidelines for Authors so make sure you read them and behave accordingly on the site.
Don't insult your agent/editor/publisher online: Even little comments complaining about edits, formatting or errors can put people's noses out. I have a friend who had their Big Six publisher make a huge error in her book. It really upset her. But I never saw her talk about it online at all. I also know of a case where an author's publisher didn't fulfil their marketing obligations and the author didn't do a peep online. It reflects poorly on you and your publisher.
Remember, agents have put their faith in you and are your advocates. Even if they're not performing for you they way you want, online isn't the place to vent. If you want to get a new agent, chances are they'll check your social media and if they see you going off about agents and publishers then it's not going to be in your favour.
Don't insult potential readers: Don't speak badly of other genres and categories - your readers could like those too. I've seen an author insult potential readers by degrading YA (why would you turn your nose up at readers of the best selling category?!).
Be understanding: Things happen. To memory I'm yet to read an eBook that hasn't had a mistake in it. Even Big Six published ones. Just let your agent/editor know and they'll deal with it.
Be aware of your obligations: There's an expectation for authors to do their lion's share of the publicist. Be ready for it and deliver. You'll have deadlines to meet. Publishing is a time sensitive industry so you need to be on the ball.
In doing some research for this article I found this great site, Pocketful of Books, that has a section dedicated to Bad Author Behaviour. It highlights some of the various ways authors have done themselves damage with poor online behaviour. Do yourself a favour, behave on line and don't get added to this list.
And here's a list for authors on how not to behave whether agented or unagented, published or unpublished.
The key to remember is online you are very visible. Someone is always watching. People will see your posts and it's likely to get back to your editor or agent. Even if you delete, people can screen shot it before you do. This has happened many times.
If you behave poorly regularly and give your agent or publisher a bad reputation, you may find yourself without and agent or a publisher. Once you have a reputation like that it's hard to erase.
Publishing is a very small industry, so play nice.