The first thing you should do is start moving things around. You never know what might start to work best for your viewing experience. Unless you have a wall-mounted TV, try putting the whole entertainment set in new places to see if it looks better anywhere else in the room, but also to see where the TV will get the least amount of glare on the screen so you get the best picture clarity. Next, try moving the speakers into new locations around the room; you should aim for a surround sound feel, so try putting every speaker in a different location, but all facing towards the central viewing area; for example, speakers to both sides of the TV, both sides of the couch in front of the TV, the back corners of the room, etc... You can even try moving furniture around so that everyone watching gets the best possible sight and sound from their location.
On the subject of sound, make sure that all your speakers are not just the same brand, but come from the same set. If your speakers are all of a different variety, the sound they produce will not be the same, that is, every speaker will be producing a slightly different sound which will be noticeable and certainly detrimental to watching/listening to whatever you have playing. Many sound systems also have left & right specific speakers, so if you have two sets of left speakers working together, you’ll be missing out on half the sounds that are supposed to be produced. It will be like listening to music with only one headphone on, you miss out on half of your songs or shows every time you play them. It may be a little pricier, but if you can, consider upgrading your home theater system to one congruent sound system.
Everyone knows that light bounces and reflects off of hard surfaces, but sound does too. If your floor is tile or hardwood, the sound is reverberating off of those surfaces before it gets to your ears, and you’re losing the purity of the sound being produced by your speakers, so do yourself a favor and buy a rug for the room if you don’t already have one. It will benefit your sound quality, make the room more comfortable, and “really tie the place together.” The next surface to take care of is the windows; if you leave those open when you’re watching TV or listening to music, you’re hurting the sound quality there too. The sound will rebound off of the windows like it does with a hardwood floor, so always make sure to close the blinds (drapes are better since they’re softer, if that’s an option) and kill two birds with one stone; the sound quality will increase, and the darker the room the better the viewing experience of the TV, if you need any proof of that just walk into any movie theater and check how many open windows they have inside and how much light there is not coming from the screen.