I just read an article offering tips on how to record good audio if you are stuck doing it in a poor room. My definition of a poor room is a rectangular room, usually a converted bedroom in your house. By definition a rectangular is poor because the way sound bounces around in one of those, you tend to get dead zones where certain frequencies are cancelled out, and other areas where certain frequencies get artificially boosted. Those things make it worse for listening (important for mixing and mastering) than for recording, really. Probably the worst thing for recording is to have bare walls, ceiling and floors that are parallel, which make for lots of echos and reverb (yeah, technically the same thing - shh!), which you don't want in your recordings.
We already have an article on this topic here - How to Build a Home Recording Studio: Part 2 – Four Tips For Preventing Noise, and actually here as well - Recording Vocals In a Bedroom Studio. Preventing noise is really what it's all about. And room echo is one category of noise.
The tips in the article I mentioned started out by saying to use a mattress BEHIND the person recording (assumption was that you are recording vocals). The logic was that the voice would bounce off the wall behind the mic, reflect again behind the vocalist, bounce off THAT wall, and then bounce back into the sensitive end of the mic. So if the mattress is behind the vocalist, the reflection off the front wall will be trapped by the mattress and not be able to bounce off the back wall to enter the sensitive side of the mic. OK, maybe. But if you put the mattress in front of the vocalist, behind the mic, the voice won't reach the front wall, so there will be nothing to bounce off the back wall. The real truth is that it will depend on your vocalist, your room, and what kind of mattress. So if you decide to try the mattress method. Be sure to try it both ways. Heck, why not try both. If you have multiple mattresses, you could build your own mattress vocal booth.
The next tip from that article is to add soft, plush furniture, which is actually sort of an extension of the mattress idea, which is to have more things to absorb the sound, the logic probably being that what gets absorbed won't be able to bounce off the walls. Again, this may or may not work. Sort of related to this is something I did once. We had a closet pole from which hung several wool cloaks (part of our medieval re-creation hobby). I positioned myself completely surrounded - almost covered - in wool cloaks. That eliminated outside noise and echo.
I strongly disagree with this one as a top tip for reducing noise. While it is true that dynamic mics offer less sensitivity than studio condensers, they also are usually (until you get into mics costing well over $300) not good enough for things like voice-over recording or lead vocals for music. The author states that the trade-off is worth it. Trust me on this one. Unless you are using one of the expensive dynamics, no it isn't. I do voice-over work AND sing lead vocals, and I do it in a bedroom! See my articles above for the countermeasures I use. It is VERY possible to do it in a poor room. No, it isn't ideal, but it definitely CAN be done. Now before I start getting hate mail from owners of really good dynamic mics, let me say that it is ALSO possible to get excellent vocal sound from certain dynamic mics, such as the Electro-Voice RE20 and the Shure SM7b. But these mics are $449 and $349, respectively. So at the very least, I would qualify this particular tip by saying "if you can afford it, try a really good dynamic mic to help reduce room noise." But if you are on a budget, you can get more bang for your buck with a large-diaphragm condenser mic, which can act as a great all-around mic. The two dynamics I mentioned are pretty much designed for vocal broadcast - for radio, podcast, voice-over, etc. But I highly recommend renting or borrowing one of these mics before buying, as it may not help much, if at all, with your particular room.
This one I absolutely agree with. It's in my list of the top things to do. In fact, I would say it should be the first thing you try. By getting your lips very close to the mic - like 2-to-4 inches - you help to sort of "crowd out" the other types of noise. Also, if you have a mic that has a cardioid pick-up pattern, close-miking can give you increased low-frequency response, which can be pleasing for voice-overs.
Like so many things in audio recording, there are very few rules that apply to everyone and every space. Try these things out and see what works best for your voice, your room, and your budget.