Tim - Over the years I've experimented with finding a GOOD VA. A few years ago I found an excellent one via upwork (then oDesk). Here is the process I used to find her.
1. I started off on oDesk (now Upwork) by posting a small task.
2. For those who responded, I used the internal filtering that Upwork provides to narrow the field of candidates. For example, look at hours worked and feedback. Pay attention to communication skills otherwise you spend too much time trying to bridge language barriers.
3. I tried a few, perhaps 3 which turned out to be too painful to work with. But the fourth one was the charm.
4. Over time I increased the range and scope of tasks. Fortunately she is a quick study and sometimes shows me tricks in excel and other programs I didn't know.
5. -->> I pay her more than her standard rate and tip her when appropriate.<<-- This works wonders in getting things done.
6. For any task, I find it easiest to create a general written outline and then a screen capture of me performing the task which is uploaded to YouTube for her reference.
Downside
1. Depending on the VA, they might have other clients they are working with. So if you need a task done in a few hours or days, you might have to wait while they tend to other clients. (I have an agreement with her that she'll get paid a slight premium for this type of work.)
2. Just like an employee, they have a life outside of their VA work. When she had her 2nd child, she communicated that she'd need some time off which was ok with me. Point here is to make sure you and the VA communicate clearly so each understands these variables.
3. While I can keep her busy with work most weeks of the year, there are a few slow times were I either can't process the work for her or we are all caught up. I tell her this so she can plan her week ahead.
4. Relying on her too much. As with any "out sourcing", there is the possibility that one day she'll no longer be available. We have a plan for this. But it would be painful if we are in the middle of a project.
In Summary
If you can survive the painful process of finding a good VA, they are worth every penny you pay them.
Hope this helps.