Recording live sound: Acoustic
Recording vocals, or any variety of acoustic instruments is as easy as the hardware you possess. Do some research into the differences and capabilities of cardioid, ribbon, condenser etc microphones and make an educated guess as to what you'll need to record you instrument of choice.
Now, you need to take some time to think about what sort of interface you'll need between your mic and your computer. If you're recording a sixteen piece drum set you'll likely desire a mic for each batter head of each drum, two mics for the bass drum and snare drum, and a compliment of overheads for cymbals, chimes, cowbells, or whatever else you or your drummer has implemented into his set. In this case you're going to want a mixing board with plenty of channels for each of your mics. If you only need to record a five piece drum kit with a small handful of cymbals, you can get by with an eight channel board pretty easily without giving up too much quality. If you don't have a drum set or drummer to worry about, then you likely do just fine without needing a mixing board, you'll just need some interface for your microphone so you can control levels and if you're using a condenser mic, a phantom power supply.
Rule of thumb number one
Once you've begun doing sound checks and fiddling with levels on your mixer, or E.Q. on whatever single mic interface you may have chosen, you're going to want to take a look at the Audacity waveform you've recorded. Is it very small? Is it so large it takes up the whole track? Either way you have some adjustments you're going to want to make. If you happen to be recording that big drum set referenced earlier, hopefully you can or you have someone on hand to go through a sound check with the board. Without having your levels set properly you'll run into issues like the snare being too quiet, or the floor tom being too loud, or this level or that level is too pronounced, or not. Whether you're doing lots of drums or just one acoustic guitar, you want the level to not clip past 0db while also not letting the level get too low. (zero db being clipped makes the waveform take up the whole track window) There are many ways of getting around this.
The cheap way is by using the built in compression in audacity. Get your levels just below clipping, select the entire track you wish to compress, and apply a tight compression. Next run the hard limiter if needed to clean up spikes in volume, then amplify to your liking. This will bring up quiet sections to closer match louder sections without allowing the loud sections to clip out.
The expensive way around this problem is to buy a compressor/limiter/gate unit and apply compression to the audio before it ever gets recorded by audacity.
Rule of thumb number two Lighting.
Yep I said it, lighting can make the difference between a good, poor, and great recording. Incandescent lights give off a low hum that is hard to pick up on most microphones, and consequently easy to erase or overpower. Those who are very 'green minded' and use florescent bulbs only may wish to record in the daytime, by candle light or in the dark. Reason being; florescent bulbs hum quite audibly, and microphones pick up that humming disturbance much better than even the human ear. If you've been trying to lay down a vocal and have been plagued with some phantom buzzing or humming noise in the background I'm going to guess that some electrical device was the culprit, and 9 times out of 10 it's a florescent light at fault. Other common suspects are cell phones, bug zappers, studio monitors (the cheap unshielded ones) and the tube amp your guitarist forgot to switch off during your take.
Rule of thumb number three
If you're looking to get a low-fidelity sound from your performance, go ahead and record it just anywhere under any circumstances. Weird Al Yankovic recorded 'Another one rides the Bus' in a bathroom. And it sounds like it. Recording a guitar by itself in a big room such as a church sanctuary might sound very nice, but recording a vocal and making that sound big and full like a studio recording in that same room won't work. (unless you want to spend a lot of cash) So rule of thumb three, section one
Vocal recording You have your microphone, your interface, and your voice. Now you just need a couple square feet of sound canceling foam (or an expensive factory built contraption). Take the foam and place it into a shallow box and mount that box behind your mic stand. This will capture your voice and not allow it to reflect back into the room, creating reverb, or echo.
Acoustic Guitar recording This is much more flexible depending on your tastes and the method with which you record. Aiming a microphone at the sound port on your guitar is usually all it takes to capture good sound, though if you have several mics at your disposal and want to experiment, put one up close and personal, and a couple in different areas of the room. Tinker with the mix (if you have that mixing board) and find a sound that strikes your fancy. If you find that you can't get a 'dead' enough sound, or a reverb-less enough sound, try the same technique described above to shield the room, and thusly the mic from sound reflection.
Acoustic drum recording It's best to have an extra set of hands/ears when sound checking a drum set, though it's not impossible to do on your own if you're willing to record drum samples, play them back, and make guesses at the mixing board till you get it right. A good starting point is the bass drum. Whether you mic it once or you have a pair of mics, the objective is to get a nice fat sound with clear attack without clipping the board or audacity. Next you want to get the snare drum to as close to the same level as the bass drum. Two mics are ideal, one for the batter head and one for the resonant head respectively, though you can get by with just micing the batter head. (especially if you have responsive overheads) Next you'll need to get all the toms to a consistent level, and take your time making sure each one is eq'ed to sound it's best. Finally your overheads need to be dialed in so that the cymbals are less loud than the snare/bass but well defined with plenty of high end attack. Just play around with your levels at this point until you have everything not too loud, but not ever too quiet. Once you've achieved this there are lots of tricks to apply to your drum tracks in audacity to make everything sound just as you want it to.
Rule of thumb four
Once you have a decent sounding, well mixed/eq-ed recording don't forget you can manipulate tracks in a plethora of ways and then mix them back together on top of themselves.
The acoustic guitar piece
If we select and 'duplicate' the whole track several times we can do some fun things. Lets make a bass line first. Select one of your duplicate tracks, run a low pass filter at a rather low level and then amplify the track. Voila, you have a bass line. Next we'll apply a hard flange to the next duplicate track and maybe a touch of tremolo. The next track we'll amplify as high as it will go without clipping. Afterwords we hard limit the track by -15db. Now lets re-amp the track to +14.9db. Now lets play around with this last track with the envelope tool to make the loud and distorted mess come front to back in volume.
The drum piece
So we have a whole drum section recorded, and now we want to make the recording sound bigger, punchier and more epic...
Duplicate the track three times. Compress the first track sharply, hard limit just enough to be able to amplify everything to just shy of 0db High pass filter the second track, this will give you a whole tracks' worth of snare and cymbals to play with levels on Low pass filter (set the filter in the middle) on the third track, this give a whole track of the big round reverberations of the toms and the bass Low pass filter (set the filter back to around 200-300hz) This gives you a track to control all the big booming lows from the toms and the kick drum especially.
Mix these four tracks to your delight, or go even further and make five, six, eight, or twelve duplicates and single out frequency ranges to completely control what punches, how hard, and when.