by I don’t think there is any question about how much dry-fire practice can help improve your shooting skills. In this video, Sheriff Jim Wilson talks about how to do it safely.
The ballistic pad that Sheriff Jim uses can be found here. One alternative to using a pad like this is doing your practice facing an outside wall of your house which has a backstop beyond it. By backstop, I mean a hill or retaining wall and not a wooden fence.
A basement wall that's underground works well too.
@Evan: That is a very good point.
Duct tape a bunch of thick, old telephone books together and still dry-fire in a safe direction. If it goes off, it will most likely be stopped. If it does go through, most of the power is gone. The ballistic pad is a better option, but rigging this up is better than nothing.