What I've discovered is this:
Your VA must be able to speak and write perfect English. That's by far the most important aspect.
If your VA has this, you can easily talk with them, give them assignments, and train them to do whatever you like.
My current hire works for $5.50 / hr and his skills were limited coming in, but he's been able to do a much better job than most with more skills because we can easily talk to each other!
Go to odesk.com , post a job for a "VA"
Sort by English skills and make sure you can talk with them on skype over the phone to verify their level of English.
If there is any grammar issues, move on to your next candidate!
Hope this helps when you hire your next VA.