Harvest when there is very little sign of any visible food or bedding remaining.
For techniques- do a search 'harvest' on the forum.

I use the burlap method of harvesting. It works best for me.

I'm with Hamilton. Use any surface with multiple holes in it. Put something the worms will like in the bottom of a bin, then burlap, window screen, garbage bag with lots of holes made by a pen, lid of bin with lots of holes in it....etc. on top of that stuff. Dump the finished VC on the surface and shine a light on it for a number of hours. If you feel like it, take some of the top VC off every so often to encourage the worms to keep moving down. I put 'new' aged bedding and food mixed with older VC to jump start the microbes. If there isn't much food in the VC you're harvesting, the worms will be looking for a new food source. (Yes, the worms can squeeze through window screening!)

You should also look up the 'side to side' method if you don't want to wait until your VC is completely 'done.' If you're not selling it, it doesn't matter if there are still some chunks of bedding.

Afterwards, you might want to think about letting the VC sit for a month or two for the cocoons to hatch and the worms to grow to a size you can see them and get them out. As cathd said, look around, there's LOTS of information on harvesting, both in the standard books like 'Worms eat my Garbage' by Mary Applehoff (I got one from the library - once you understand the process, you don't need to keep the book), and on this site and other vermicomposting sites. If you're having trouble finding info here (which you shouldn't), or want more info, check out redwormcomposting.com and vermicomposters.ning.com. I hope this kind of 'advertising' isn't frowned upon!