Hello,
You need the knowledge of a variety of courses.
As you can see, from the list below, this is quite an enormous stuff to study, understand and practice. I also do praparation for certification.
I buy some books from SAP Press additionally. 
Some books of SAP Press.com now available for ebook readers. For studying in the spare time 
I also do practice on SAP test enviroment more than one time. So you can imagine a time consuming "job" in the spare time.
I also do a lot of research on SAP Community Network, too.
all the best
Erwin
