An incomplete and ever-expanding list of basic buying, setups and usage tips along with some insight into hardware specifics and which numbers actually matter when buying audio equipment.
1. Don't Buy Audio Equipment from TV Manufacturers - 99% of the time a company like Sony, LG, Vizio, Westinghouse, Panasonic, Samsung, etc don't invest their profits back into their audio lineup. They R&D tv's and phones and answering machines and audio gets very little love. Sony is the only brand that has passable headphones and peripherals.(Don't buy their amps!). This is a general rule and easy to remember.
2. Ignore Wattage on Both Speakers and Amplifiers - MOSTLY *Only on the rarest occasion will wattage actually play a part in getting the most out of your setup. On average no more than 10-15 watts is used to play even the largest floor-standing speakers and since wattage is logarithmic gain where you need to at least double it to have even a 3db bump. That said you never want to drive an amplifier at full tilt, ever. If you find yourself doing this you may need a bigger amp or more efficient° speakers.*
*Speaker Efficiency is usually written as the value Sensitivity. It tells you how loud you can expect your speaker to get and is measured with 1 watt of power from 1 meter away. Higher than 90db is considered very efficient, lower than 90 isn't and means your speakers are hard to drive loud*
3. Placement is Everything - *Even the cheapest logitech 2.0 or samsung HTiB speakers can be improved if you simply place them in the right spot. A good starting point for Stereo 2.0 is this for 2.1 the same rules apply only you need to consider sub placement. A 5.1 setup works best like this and a full 7.1 expands on that to look like this. Keeping everything at ear height or slightly higher is always my recommendation.* Want a Bit More Insanity?
4. The Room you are in Matters - *This falls into the same category as the above rule. Placement around the listener is important but placing speakers in an all-Italian Marble bathroom is MORE important. Sound bounces. It hops skips and jumps all around you. This can be very very bad and ruin even the most impressive speakers. Huge empty room reverberate and hit you with the same sound 50 times in a fraction of a second. Fight this with carpets, Furniture and if needed seek out or DIY acoustical treatments which can make a BIG difference (note this video isn't showing a very good or practical job)*
5. Audition Speakers if you Can - *Playing speakers on a shelf in a best buy doesn't tell you a damned thing about how they are going to sound in your den, living room, on your desk or any place else. Higher end audio shops will usually allow you to test speakers in your own home before you flat out buy them. Other big retailers you may have to check return policies and purchase with the full intention of taking a set speakers back in a week. Any way you test be sure to listen to music you are familiar with so you know exactly how a set of speakers sounds compared to what you have heard previously. The radio or a demo CD you don't know can cloud your judgement*
6. Wireless is a Four Letter Word - *Running wires for a rear channel or to get analog signals across a room can be awkward, difficult and sometimes ugly. BUT the audio benefits, cost savings and extra work will ALWAYS outweigh the... Well there aren't any benefits going wireless. You see it is impossible. If you wanted wireless rear surround speakers you will at some point be plugging in a transmitter behind your AV equipment and then one or BOTH speakers to a wall outlet which has far more constraints than just hiding some 16ga zip cord along your moldings. You also have to deal with Audio encoding/decoding via wireless (digital low bandwidth or Analog and noisy) and amplification that will most certainly be sub-standard and housed inside the speaker or in a small plastic box. So you still have wires and you can't customize the length and it will sound worse. Case Closed.*
7. Soundbars are a Very Bad Thing - *Although Convenient and Sleek, A bar <40" wide cannot perform as well as even two small bookshelves placed in a proper stereo position which will give far more presence and soundstage in comparison. The fact that the bar is usually made of plastic is a poor choice as I don't know of any Violin's, guitars or piano's made from that material. A speaker is the same as any instrument and what it is made of matters. Now include an amplifier small enough to fit inside said bar and mount it flush against a wall with no breathing room and you will just start to scratch the surface as to why they are bad.*
8. Home Theater in a Box Systems Suck - *First they are usually by those brands we discussed earlier (TV manufacturers). Second the receivers tend to be below the bottom of the line for even respectable audio companies (Onkyo). Lastly the speakers and subwoofer are the worst, cheap, high-fashion garbage and hold no love in this world for you or I. These setups also lack even basic features and inputs found on a run of the mill ~$250 entry level Standalone receiver and usually have very over-rated and dirty power (1,100 watts my ass) so changing to real speakers instead of the plastic garbage can damage both parties. If you want 5.1 and can't afford a real one. Start with Stereo and move up. This post (http://www.reddit.com/r/Zeos/comments/10e7xq/how_to_buildup_a_51_system/) helps with that.*
9. Don't be Afraid to Buy Used - *A $1,000 set of speakers/headphones/amplifiers bought brand new five years ago will still sound as good as $1,000 speakers/headphones/amplifiers but will cost a lot less! Most hardcore audio people like to try and experiment with as many different setups as they can and will buy new equipment once a year, two years, six months. Keep an eye out on craigslist, ebay, audiogon and /r/AVexchange for deals on speakers that might give you a leg up over what you can buy new. Don't think that used means obsolete or broken, it is just used.*
10. Distortion is the Enemy - *A 1,000 watt amplifier means nothing if the Total Harmonic Distortion (THD) of said amp isn't listed or IS listed and is horrible. A high THD% means you can get metal out of your speakers when playing smooth jazz. A THD% should be posted on all decent amplification equipment and a value under 1% is acceptable (barely), under 0.5% is good and 0.1 is great (Note some ClassD Digital amps can maintain very low distortion at wattages under full and skyrocket to 10% at full power!)*
11. Ohm's (Ω) explained like you are 5 - *Imagine twisting your speaker wire ends together with no speaker. That would be the equivalent of a 0Ω speaker connected to your amp. After doing that your amp would get toasty warm and catch fire. This is because all the power it is sending out it is getting right back.. and out and back and out and BOOM. A violent cycle. What you need is a speaker to absorb that power and only send a fraction back to the amp. How much power your speaker eats is dependent on the ohms. 2Ω is very little so the amp still gets a load back and only a SUPER high power/quality amp will be able to run it. A 4Ω speaker is easier to drive than a 2 but still requires a good amp to handle and most AVR's won't do without special care. 6 to 8Ω speakers are the "normal" or average you will find. They are relatively easy to power and most bookshelves and towers fall here. HTiB speakers usually either run a higher OHM speaker so the built in amplifiers can have an easier time or a Lower OHM speaker to claim 1,000,000 watts.*
12. Bigger Actually is Better Sometimes - *It is hard to define this one as it applies to many items. Small speakers often sound small and limited, but at close range this may work fine. Trying to put small speakers in a BIG room or far away means you are mis-using them. The bigger the room the more air you need to displace to have sound travel across it properly. The same with subwoofers. An amplifier that is very small MUST be low power because to make clean high power an amp needs space for BIG cooling and a BIG power supply
13. Don't buy Expensive Cables - *Some wires you buy because they are built well and will survive a year or two of getting yanked and pulled, that is fine. On the other hand sometimes people will try to sell you wires that make things sound or look better. When in the digital realm don't bother. HDMI, COAX-Digital and Fiber Optic wires are either working perfectly or are broken. Never better or worse. Analog wires like RCA's, 3.5mm headphone wires and speaker cables can require a better quality than any-old-thing but never as much as you are told. Monoprice.com often has cheap cables that will do an above-distinguishable-from-expensive-cables job. Also power cables don't matter, 110V and low load items work on anything and don't effect actual sound quality. Most interference can usually be contributed to power issues and a UPS or power conditioner can help.*
Any suggestions to add or correct the rules feel free to post.