This is possibly the coolest music video ever made!
The outgoing Commander of the ISS singing "Space Oddity". In space.
Setting up speakers in a room for optimum sound quality is both a science and an art. The science involves things we know about how room boundaries and various surfaces interact with sound, and how human hearing works; the art consists of trying creative solutions and judging what works best for you by ear.
(An early draft of this "How to" piece was originally written to appear as "Burning Question: How should I set up my speakers?" in Wired magazine. I was paid in full, but the piece, sadly, never appeared, and eventually the rights reverted back to me.)
Whether you have an inexpensive stereo, or tens of thousands of dollars invested in a two channel system or home theater, the single biggest factor in how good it will sound is where you put your speakers. Poor locations will spoil the sound, while careful placement will bring out the best your gear is capable of.
First, read any documentation that came with your speakers - some are designed to sound best when placed against a wall, while others aren't, for instance.
Be prepared to consider and experiment with even the oddest positions, just in case they are your perfect solution. The fun part of optimizing speaker location is that you get to call it "work", and yet spend all your time listening to music.
Choose some examples of music you like that are well-recorded to use for testing, and pick a few tracks to use as benchmarks at each stage of the process.
Place your main front speakers equal distances away from your video screen, if you are using one. Face them towards where you usually listen from. If they are small, set them up at approximately ear height to start. At this stage, experiment with location using whatever means you have - chairs make excellent improvised stands, and books are useful for small height changes and tilting them.
Now, put on your music, and try moving the speakers further apart and closer together to hear how that affects the sound. Move them forward and back, too. Alter their height a bit and listen to what that does.
Pay close attention to the sounds we are most familiar with, like human voices - do they sound more, or less, "natural" in a given set up? Listen to the bass, and make sure that different notes play with equal volume and clarity. Does the music sound like it fills the space between and around the speakers? Does it make you want to dance or sing along?
There are two ways that speakers can be angled to improve the sound - aiming them inwards (or outwards) a bit, and tilting them backwards (or forwards, if they are up high) a bit. You now have a small arsenal of tactics - altering separation, height, distance from you, and two angles - and it's just a matter of slowly combining the best results for each option.
You should try to set up both speakers similarly - the same distances from walls, for instance, and at the same height and angles. If, however, your room is odd-shaped, this may not work best. Part of speaker placement can even involve rearranging the furniture to make the room more symmetrical, preventing the objects in it from unevenly reflecting or absorbing sound waves that are meant for your ears. What this achieves is balance, in that any effects your furnishings and placement have on the sound of one speaker will affect the other speaker the same way.
Some arrangements may not be practical: given the choice between a happy marriage and a speaker "perfectly placed" in the middle of the living room, with all the furniture pushed out of the way, the best option may not actually get the best sound possible.
These techniques also apply to any surround speakers you are using. They are usually positioned higher than the front speakers, and on the side walls rather than the rear wall. A center channel speaker should be close to your screen, centered above or below it (try both).
As you zero in on the best locations, you should hear a marked improvement in sound quality, and the overall sense of the music being made "in the room" rather than being played "at" it.
Once you dial in your final compromise between decor and sound quality, it's time to invest in making their positions stable and permanent with well-made stands, shelves, or brackets. Stability is important for both safety and sound quality. You don't want your speakers falling on anything, and they will sound better if they are not wasting your amplifier's power by shaking their cabinets instead of your booty.
By applying and enjoying this process, even a modest system should produce great sound, and an exceptional one will be breathtaking. The final "test" of the results is whether you find yourself listening to more music than you used to - and singing along.