So I am going to tell you how to play with your teeth, this is going to be a short guide and it will not be perfect. There is also a very short explanation of sweep picking but if you want to learn it properly I suggest looking at one of the many sweep-picking or sweeping lessons on UG.
Warning: Do not try this if you have cheap strings (they may get damaged) or are wearing braces (it will hurt).
This is not going to be a very long lesson but playing with your teeth does take ages. It's pretty dangerous, a string could snap, you could chip a tooth, you could scratch your pickups, the list is endless. I've tried to avoid some of these problems by not actually 'playing with my teeth', it's just as good.
To play with my teeth I hold the pick in my mouth and play. This is safer that picking with my teeth itself as you’re less likely to chip a tooth and it doesn’t leave the taste of metal in your mouth, which is defiantly a bonus.
Summary Of This Lesson:
Part 1: How To Hold Your Guitar
Part 2: How To Strum/pick
Part 3: Sweep Picking (simplified)
Part 4: What To Play/make
Part 5: Conclusion
Part 1: How To Hold Your Guitar
I must point out that this is for right handed guitar players (people who normally strum with their right hand) because it could go horribly wrong if you didn't know, if you’re left handed just reverse most of this.
Hold your guitar so the back is facing away from you, the rhythm and treble switch is at the bottom (if you have one). Your left hand holds the frets so your thumb balances the freeboard and your main guitar playing fingers can reach over the top. Your right hand is used to hold the guitar up, grip tightly round the bottom of your guitar. If you have a heavy guitar you will need to practice lifting it up into this position before you play it in front of people. Dropping it in front of your mates and smashing your guitar or toes is pretty embarrassing, it’ll also sound awful.
Part 2: How To Srum/pick
Now you know how to hold your guitar it's time to learn the details of how to play the strings. There is a couple of ways to do this; I choose to do a combination of 1 and 3.
1) Move your guitar up and down so the strings move over your pick, you must keep your head still for this to work.
2) Hold the pick with your top teeth slightly in front of where your bottom teeth are holding it, move your teeth slightly so the pick wobbles.
This is probably the hardest method as it's easy to drop the pick.
3) Keep your guitar still and move your entire head, keeping the pick in the same grip inside your mouth, move your head over the strings to make them work.
A slight adaptation to part 1 is that you can tilt the angle of your guitar instead of moving the whole weight of it up and down continuously although I wouldn't suggest it as it is surprisingly difficult. For all of these I would advise you to use sweep-picking wherever possible, if you don't know what it is I’ll explain in part 3. Also for this you will need to have your pick at an angle so it doesn’t get stuck between strings. You will also, as with sweeping, need to hold it not quite as tight as you would think so that the pick glides over the strings more smoothly (but try not to swallow your pick as that would be a bit of a problem).
Here's a simple exercise that you can use to practice this, try to increase speed as you go along.
e|-2-----2-2-----2-2-----2----|
B|--3---3---3---3---3---3-----|
G|---2-2-----2-2-----2-2------|
D|----------------------------|
A|----------------------------|
E|----------------------------|
Part 3: Sweep Picking
Sweep picking is a type of picking that allows you to pick adjacent string (strings that are directly next each other) easily. Sweep picking (or sweeping) is pretty hard to do but a relatively simply concept. I'm not exactly an expert but here’s a simple guide on how to do it.
1) Hold a chord with your left hand (optional, but don’t make this hands part to complicated)
2) Hold your pick loosely
3) 'Glide' your pick over the strings without lifting it up in-between strings.
This is obviously slightly different when played with the pick in your mouth but you can still use the general idea; slide the pick over the strings loosely without moving it away in-between to make playing adjacent strings easier. You will also need to decide whether to use up or down strokes, I suggest using the same for each 'phrase’ sequence so you don’t have to keep thinking about it. Do not try alternate picking, you’ll fail.
Now try the same exercise as before, it should be easier. "u" means up-stroke and "d" means down-stroke…
ddd uuu ddd uuu ddd uuu
e|-2-----2-2-----2-2-----2----|
B|--3---3---3---3---3---3-----|
G|---2-2-----2-2-----2-2------|
D|----------------------------|
A|----------------------------|
E|----------------------------|
Part 4: What To Play/make
Here are a couple of things it's best to avoid when choosing/making a song to play with your teeth. These are not rules, only guidelines.
Avoid
1) Jumping lots of strings at once
2) Making your left hand part too complicated
3) Really long songs
4) Too much speed
5) Heavy guitars
6) Jumping lots of frets at once
Include
1) Small string changes
2) Arpeggios (broken down chords)
3) Rests
4) A mixture of chords and individual notes
As I said before these are just guidelines. A green light won’t zap you and turn you to stone if you ignore them (though that would make a cool music video).
Part 5: Conclusion
Here’s what you should have learnt, If you haven’t re-read it or blame it on me and give me a bad rating.
1) How to play with your teeth (but not be an expert, which comes with practice)
2) How to hold your guitar for teeth playing
3) What sweep-picking (sweeping) is and how to use it for teeth playing
4) Some guidelines on what to play.
/ my profile 
