(Note: Asking questions also counts.)
System Administration requires a diverse set of skills that (still) most pick up on the job in a reactive way: Problem occurs, learn what is needed to solve it; if we like the subject dig deeper too. Serverfault is one of those places where people in the profession go for help. Reading questions and answers helps, but answering something helps more. Actually writing an answer (or a question) includes that extra effort that differentiates between it may be solved this way and it is solved this way. Plus there is a whole community that can correct in no time any errors in your answers. You do not even have to know the answer. Just pick up any question you find interesting enough and try to find an answer. The diversity of the questions asked on serverfault makes it virtually impossible to not find at least one (even remotely) interesting every day.
Just pick one. Any. Failure is an option. You do not have to be sysadmin1138 to answer a question, but you can surely become one.