Even if it's just an inexpensive iPod or Bluetooth speaker, careful placement can really make a difference in the sound. Specific placement requirements vary with the type of speaker, but it's usually wise to have speakers at least 36 inches off the floor, close to the height of a seated listener's head. If the speakers have to be placed lower or higher, angle them toward the main listening position. Try to place speakers at least a few feet away from corners and large pieces of furniture that reflect sound.
Placing speakers close to boundaries -- walls, corners, floor, or ceiling -- will maximize bass output. The downside to that placement strategy is a lack of treble detail. One of the worst-case placement scenarios I heard about came from a speaker designer friend. He once saw a pair of his speakers on the floor, under a table covered with a tablecloth! Another friend bought his dad a pair of small high-end speakers, and his mom tucked them under the couch, hardly the best placement strategy! I've also seen short tower speakers used as end tables on either side of the couch, and stereo systems with the left channel speaker in the kitchen, and the right channel in the bedroom. Great sound, even with the best speakers, won't happen with suboptimal placement.
Home theater systems have the most speakers, so they're the most demanding in their. Speaker diagrams may look nice on paper, but in the real world a lot of folks just put the speakers where they can. I've seen more than a few home theater in a box systems with all five speakers placed in a single row under the TV.
If you're using a non-standard placement orientation, tell us about it in the comments section.