There are many skills and tasks one can master in order to become a successful Administrative Assistant. One area an assistant must know are computer skills. Here is an article that will touch on the clerical side of the job.
Probably the most basic, yet the most important. Typing is probably the most valuable skill an Administrative Assistant can have. There are various software programs that you can use to practice your typing skills, and if you go through a temp agency or a recruiter, they will more than likely test you on your typing skills. For entry-level jobs, you will need to be able to type at least 35 words per minute ("wpm"). A more advanced position will require somewhere between 60-80 wpm.
I've noticed this skill is not as critical as it once was, maybe because most calculations these days can be generated through spreadsheet software. But it is a good fundamental skill for every Administrative Assistant to know, and it's critical if you are a Data Entry or Accounting Clerk. As with typing, there are software programs and classes that let you practice and master 10 key skills.
Aka "People Skills". It is critical that every Administrative Assistant be flexible and have the ability to interact with every personality out there, more than most any other job around. It is a great skill to have and probably the toughest to master.
Another basic skill that every Administrative Assistant needs. If you are not an organized person but you want to be an Assistant, it is probably a good idea to take a class or a seminar on the topic. This includes both offline and electronic organization.
This includes excellent grammar, ability to spell, and the ability to communicate effectively. If you have a boss that possesses none of these qualities, that does NOT mean that you can slack off in this area! In fact, yours has to be that much better, since as an Administrative Assistant you represent your boss.
Time Management Skills
An Administrative Assistant knows how to manage her time effectively as well as her boss' time. This includes using tools such as Outlook to keep track of schedules or paper time management organizers such as Franklin Covey organizers.
This is simply an overview of the skills that all Administrative Assistants (and other support staff) should possess to have a successful career.