Well, first of all you need to have a genuine interest in 'dba:ing' (whatever that is) 😉
As with everything else, you want to learn as much as possible about how the stuff works.
I assume there are several books on the subject as well.
Personally, I deal with stuff as;
Hardware: - you need to be proficient with hardware, and preferrably learn how to build a server designed to support different database requirements. This is a really huge subject on it's own.
Everything from cpu, memory, designing disksystems etc... Very important to 'get right' for any succesful database implementation
O/S: - It's good to know how the universe we live in works. Knowledge about what makes Windows tick, is never a disadvantage, especially secuity models and such. A very high percentage of problems has it's roots in permissions at some level. Many times the DBA need to be aware, or solve such scenarios.
Network: - you need to know basics about how a network works. After all, we're in enterprises nowadays, and the network is the glue between everything.
Relational Theory: - you need to understand what a relational database is all about. What is 'good' and what is 'not so good', and the principles behind it all. This is key to understanding SQL and modelling.
SQL: - Learn and understand to program in SQL. This involves tri-state logic, set-based thinking and a lot of things not encountered in other programming languages. SQL is in this repsect one of the most powerful languages existing - easy to learn, very difficult to master. But is absolutely essential for any DBA.
Modelling: - This deals with entities, normalization, cardinality and a lot of stuff from relational theory.
Also a very large subject on it's own.
So, you're in for a handful 😀
The best way is probably just to start using all of it, find some 'starting dba' book, browse through BOL (Books On Line - the online SQL Server 'manual'), scour the net for database forums (like this one) and read as many posts you can. Bit by bit with time you'll start to get a grip on what it's all about...
And it's never wrong to as a question when in doubt.
Good luck. 🙂