Vocal percussion has its roots all over the world; before it was American, it was from the south of India, and Africa. In addition to being great for you mentally--since you have to be able to listen and hear drums precisely--it's also an aerobic exercise that can make novices pass out or at least get very dizzy. It breeds nice abs and good blood pressure, and makes a neat party trick. Some day, I would love to meet a true vocal percussion guru. Maybe he will show me the Cowbell.

Until that day, I place my manual for beginners here. Don't be afraid to spit on the monitor.

Audio examples of me, qeyser, and GS_Threeve percussing in the studio with lyric are available at http://centaur.acm.jhu.edu/~lyric/huh/ (for the time being).
The Basics

Fair warning: vocal percussion is a lot of fun, but it really annoys some people, and when you've done it long enough, you won't even notice that you're doing it. This could be a bad thing if you're in a business meeting and get Stairway to Heaven stuck in your head. As VT_hawkeye notes above, you will also tend to spray spittle all over the place. Needless to say, this makes the habit unattractive to some people. That said, here are the most basic steps of beginning to be a vocal percussionist.

  1. Listen to music with drums in it; I recommend Led Zeppelin, The Who, and The Rolling Stones, whose drummers were masters of the craft, but any band with a decent drummer will do. Alternatively, you can listen to rap, which occasionally has complex beats that are repeated ad infinitum throughout. Some of the best rappers of all time sample the drumming of John Bonham, though, so why not go with the original? I don't recommend pop, especially today's pop, because the beats are dumbed down and thinned out so much that they're no more expressive than a metronome. If you're honestly serious about learning vocal percussion, music with real drummers needs to be a part of your life.

  2. Find your diaphragm. If nobody can hear you, what's the point of percussing? I do not advocate listening to the atrocity that is Who Let the Dogs Out, but barking in that manner will teach you some diaphragm control. Anyone who was in the military can teach you to bark an order from the diaphragm, too; officers and drill sergeants may have a little more practice. For a live-fire demonstration, say the word "Hua!" loudly to any Marine, and listen to the response. If you didn't notice any difference between yours and theirs, say "Hua!" again, a little louder than the Marine did. When the Marine has sufficiently motivated you, go practice saying "Hua" in front of a mirror, and watch your belly when you do it. After a little practice, you will feel like you've been doing sit-ups and your abdomen will be a little sore. This means you're doing it right.

  3. Start with a simple bass drum. The words "doo" and "boo" (with the "oo" coming from the gut) are syllables that will last you the rest of your days. They are ubiquitous, omnipresent, and also really important. If your voice tends to be a bass or baritone voice (for men) or a tenor or alto (for women), you will have more luck with getting an authentic bass drum flavor to your sound. Once you have the start of both the "D" and "B" bass drums, try pinching your lips around the "oo" sound so you get "Doof" or "Dfff" or even "Bvvvfff" from the rapid airflow.
    I'll pause here to note that my transliterations of the sounds are not ever going to be exact, because drumspeak never is; as with all communication, you need to be able to meet the communicator halfway.
    These bass drum sounds will form the root of every beat you create. Practice these by listening to any rock music (or any music in simple 4/4 time) and making your bass drum sound when the drummer makes his. When the Levee Breaks, by Led Zeppelin, has the epitome of all bass drums in it, and makes worthy practice.

  4. Listen to more music with real drummers in it. Like noding, it's much easier to do well when you've watched the experts do it. Unlike noding, you can practice it in the car. Then again, noding doesn't get spittle on the inside of your windshield (or windscreen for our UK brethren).

  5. Learn your struck snare drum sounds. These are generally formed with the consonant "K" or "P" or "T"--notice that "P" is a "B" with no vocalization, and "T" is likewise a "D". A vocalized "K" is a "G", and I don't use them for my bass drum--they're just awkward. But you're welcome to repeat step three with some "G" sounds--I'll leave it as an exercise to the reader. Unlike your bass drum sounds, the vowels should not be vocalized. When I talk about a "Kah" snare (my personal favorite), it's really the letter "K", kicked out of my mouth by a diaphragm hit, while my oral cavity is shaped like I'm going to say "ahhh" for the doctor. Try a few of those, and don't vocalize. Mix in some "T" and "P" snares, and when you've got those, begin pinching off the ending for a smooth "Tfffff" or "Kfffff" sound. This may be easier than leaving it open for some folks--that's good, but you need to be able to do both. To practice your snare, I recommend Ants Marching by the Dave Matthews Band. You can ignore all the funky stuff Carter Beauford is doing with the cymbals and woodblocks... for now.

  6. Go back to your radio for some more music. This time, practice laying both the bass drum and snare drum over the drummer's line. You may be able to visualize the beat, even if you don't read music, and if you can, you'll see where cymbals should be. If you've got an inclination for mimicry, you may already be adding in cymbals. Great! If not, read on.

  7. As Phish so eloquently put it: "What is a band without cymbals? Cymbals are grand!" Add a closing "s" or "sh" to any of your snare sounds, and you've got a cymbal. You can also make the sound of a high hat cymbal while you inhale, which will be useful when you start to have all four (or three, or five, or...) beats covered in a measure. These can be sustained for a big crash cymbal effect, or pinched down to almost nothing to make a nice tight ride cymbal. If you're not looking for sustained sound, you don't need your diaphragm for these--try to do a long series of "Ts" cymbals, one after the other, and you'll see the only limit is the amount of air in your lungs. To fix this, learn to make an inhaling cymbal: touch your tongue to the roof of your mouth, smile with your mouth open, and breathe in quickly. For breathing lessons, you may want to learn some correct tuba playing techniques, but with a sharp inhalation, you'll get a satisfactory cymbal sound with minimal effort. There is a huge amount of variation available in all of these sounds, so experiment and have fun. If you want cymbal practice, Sting's Shape of my Heart is a beautiful song that can be done well on a number of experience levels.

  8. This is where the road forks. Depending on what you like to percuss to, you'll want to learn how to do woodblocks, snare rolls, toms, bongos... the list goes on and on. If I get good feedback on this node, I may tack on my methods for other sounds later, or add other mini nodes to it. The best advice I can give is to experiment with shaping your mouth, changing tongue position, or mixing in a rolled (Spanish) "R". When you've got the core of your sound toolbox together and some extras, move on to building beats.

  9. This is sort of your belt test, but it's also very practical. Well, as practical as vocal percussion gets. Pick a song, listen to it over and over, and learn its beat inside and out. Good beginner pieces include anything by AC/DC, Aerosmith, or The Rolling Stones. Make sure the sounds in the song aren't too complex for you, and begin building a vocal percussion beat out of this song. Most songs in 4/4 time will have a basic structure of "Doo (x) Kah (x)" where (x) is a cymbal or other sound. Try substituting different kinds of bass drum. When you've figured out what sound best imitates that drummer's bass drum on that song, move on to the snare. Once the root of the beat is firmly in your mind, move the cymbals and extras, and find a place that you can add an inhale cymbal or a silent breath. Once you've built up a beat that you can cycle without having to stop for breath, loop it, and start doing it along with the song.

  10. You may have noticed that the drummers aren't always playing a straight beat--they change it between the verse, the chorus, and the bridge, and every 4, 8, or 16 measures they go temporarily insane and do "some crazy stuff with, like, every drum in their kit, man." That's a fill. They separate the good from the great from the godlike. Learn to duplicate those, learn to make up your own, and learn when not to use them, and complete is your training. A Jedi you will be. No, just kidding--you won't even be a Perl ninja. You'll just be another vocal percussionist, loose on the streets of your city, spitting and twitching every time Rock and Roll comes on the radio. But you'll be a good vocal percussionist. They will be annoyed, but they will also be awed.

this node is still far from complete; suggestions are welcome.