Make sure the "digital audio output" on your DVD or Blu-ray Disc player are set to "Bitstream" and not "PCM" when making a digital audio (optical/coaxial/HDMI) connection to your receiver.
Make sure, if you're using a powered subwoofer, to set all of your speakers to "SMALL" and the subwoofer to "YES", no matter how big your speakers happen to be.
Check your "LFE" (subwoofer) crossover settings in your receiver and the back of your subwoofer. Make sure they're set to the same frequency. You want your speakers playing 100Hz and HIGHER while your subwoofer plays 100Hz and LOWER.
Make sure the "DRC" (dynamic range compression) is turned OFF, no matter how angry your neighbors get. A well-recored movie won't need any help bringing out the on-screen dialogue.
Make sure you select the highest-quality audio track on your current disc every time you put it in the player as it will usually default to the lowest quality format for backwards-compatibility with older Home Theater systems.
Check THIS LIST to see if any of your DVDs at home are "THX-Certifed". Then take a look in the DVD's menu for the "THX Optimizer" (it might also tell you on the back). The free test patterns will help you adjust your TV to near-perfect conditions.
Click right HERE to get a pair of "blue filter" glasses.
Take a look at the THX test patterns (and instructions) and how to access them below:
Do not use the "computerized" sound perimeter setup. Start with everything at "zero" and try to set it up yourself. The "auto setup" feature is only needed if your speakers are not all the same make and model and/or they've been placed improperly throughout your living room.
Turn off the "THX processing" if your receiver has it. Listen to your movies and music without the infinite number of DSP modes on your receiver running.