Some tips from allthingsorganic.com for good "happy" worm bins.
These are a few good practices for the new worm bin. If you do these, you need not worry about having any significant problems.
Do not add water to the worm bin unless a large part of the bin material lacks water. Some worm bin manufacturers suggest that water be poured through the worm bin and captured for use as "worm tea". The problem is, this is leachate, containing undecomposed food waste.
Dig under the bedding now, and every few weeks, to peek at the bottom-most material. If even a little bit is becoming waterlogged, that's a sign that you need to promote more aeration and/or drainage.
Smell the worm bin. If there's any foul odor, think "what did I add or do differently, recently, that could have led to this odor?" I once caused a terrific stink in my worm bin by adding some fermenting barley I'd picked up from a brewery.
Check to see that the temperature remains reasonably good. With changes in season, and the amount of sun that shines, a worm bin can change temperature significantly. Watch out you don't cook the worms!
Watch for worm predators if this is an outdoor bin. Moles find worms delicious, as do birds and some dogs! Make sure the bin has a lid (and a secure bottom, if necessary for your location).
More good worm advice