Thought it's helpful to read again and again.
Be on fire. You have to want to learn everything, do everything, consume everything. So you got the DBA job, now is not the time to rest in your new chair and enjoy your success. List out your goals and what you want to learn. A five year plan is a great idea.
Listen! Ask Questions! Be involved! Don't just sit back waiting for the create table requests.
When it comes to theory, don't believe anything you hear or read until you have tried it yourself. Database rule number one, in my opinion, is that no rule of thumb applies all the time.
If you are solely responsible for a database, make darned sure, before you leave your job on day one, that your database can be recovered. Nothing else matters if you can't get that database back.
And, a baker's half-dozen...
Learn to use your voice of authority. You are the DBA, and this database is your responsibility. As you learn the right way, and the wrong way to do things (like, say, database design), you need to be an advocate for best practices and for good design. If you succeed, you can enjoy the rapture of success. If they don't listen, you will get the joy of "I told you so."