Just because you've only got two speakers and a subwoofer doesn't mean you should just place the speakers wherever there's space. Audio firm Dolby offers an interactive app that shows the best speaker setups, angles, and distances for your living room.
Choose a 2.1, 5.1, or 7.1 setup from the main menu, then give Dolby the rough distance of your couch from your main viewing TV. You'll get back a diagram showing the best angles, distances, and configurations of speakers and subwoofers around your room. For those who are just getting started in the realm of home theatre, Dolby also explains the role of each speaker, so you can determine, for example, why your shows' dialogue seems so quiet while soundtracks are thrumming loud enough for your neighbours.