Bird houses can be cited throughout the year, and - in fact - this is one of those easy to do things as it's hard to get it wrong. What you can get wrong, though, is where to put up bird houses. See this article for more info. However, if you haven't got time to watch it...just please don't put one up in full sun for obvious reasons.
Haith's have an annual event for bird houses which is called "Help to Fly!" It works like this: Haith's pay half towards the cost of a basic wooden nest box meaning that garden birders' only have to pay one of the bird houses usual cost. If you'd like to know more about how that works, here's the place to read all about it.