When I started playing slide I had a hard time 'cause I could never find someone to how me the basics. There are a few a few lessons in the slide directory but none of them really tell a beginner how to play slide. I'm hoping that this lesson will give you that and get you started on a great part of guitar playing.
Before You Start
1. Your Slide.
There are two main types of slide -- glass and metal. Glass gives you a warmer tone than metal and is lighter, however it can break if it is dropped. Metal has a brighter tone than glass and is heavier, but is practically indestructible. Keep in mind that there are different types of metals used for slides and each type will give a different tone. As well, the thickness of the sides of the slide affects your tone -- thicker sides give you a bigger tone and vice versa. There are also various lengths of slides and different diameters for the inside. Yes, there are many variables but slides aren't very expensive (generally they range from about $5-$25) and you should just experiment with different kinds until you find what you like. Also don't rule out different materials like ceramic, plastic, or bone -- I just have only used glass and metal and don't want to write about something I don't know much about (if anyone cares I'm currently using a medium length Dunlop glass slide with thick sides).
2. Your Guitar.
Got a guitar with crappy intonation and strings a mile off the fretboard? Or a few bum frets? No problem! This guitar will work fine for slide because you don't really use the fretboard for slide (unless of you'r fretting notes behind the slide -- more on that later). In fact a great use for a guitar that is hard to play normally is to make it a designated slide guitar. Just watch out for crappy tuners if you're gonna be using a bunch of different tunings. This works fine if you just want to dabble in slide but if you're gonna be playing it seriously you should get a good guitar to set up just for slide.
3. Your Set-Up.
You will have a much easier time playing slide if your guitar is set up properly. Because you don't want your slide to touch the frets you want heavy strings (12s or 13s) and high action. However if your gonna fret notes behind the slide (more on that later) you don't want too high action and heavy strings make it hard to play normally. I play a Fender Telecaster with '10s and medium high action. If I had another guitar I'd probably put on heavier strings and raise the action a bit. However I don't have too much trouble on what I have as long as I don't tune down (i.e. put it in open G or D or a tuning where some of the strings have their pitch lowered) because that will give me less to support the slide.
Slide can be played in just about any tuning. Open D (low-to-high D, A, D, F#, A, D); G (D, G, B, G, B, D); A (open G up a whole step) and E (open D up a whole step) are common but you can even play in standard. Personally I recommend using open E which has been used by such legends as Sonny Landreth and Duane Allman, but it is important to know a variety of tunings and when to use them.
You can use a pick for slide but I'd recommend trying fingerpicking either with your bare fingers or using fingerpicks. Not only does this give you more tonal options but it also allows you to mute with your fingers (more on that later).
I don't want to talk about this too much because I know that tone is subjective but something I'd recommend is having your tone all the way down (the least trebly possible). The reason for this is that slides normally will brighten up your tone and if you have your tone high up you'll get a really bright screechy tone. With your tone down you can get a really nice warm tone. I want to stress that this is just something that works for me and there is no reason why you'd need to do it. However, if you're having trouble with your tone I'd recommend you give it a try. Another thing, don't overdo it on the distortion.
Now you're ready to start playing!
To get started put your slide on a finger. You can use whatever finger you find comfortable but I would recommend using your third or fourth and not using your first as this does not allow you to use a fret hand finger for muting. I find that the third finger gives me more control and better intonation but it doesn't allow me full use of my other fingers, which the fourth finger does. Use whatever is comfortable but I recommend using your pinky as it gives you much more freedom. When you play slide you just lightly touch the strings. Do not press down. You do not want to touch the frets or fingerboard.
One of the most painful things in the world is bad slide playing. Most of this is due to bad intonation (meaning not having your notes in tune). The thing to remember about intonation is play right over the fret. This is the single most important part of playing slide. The only way to improve your intonation is lok at where your playing and listen to whether or not your notes are in tune.
Without plucking any strings rub your slide against the strings. You'll hear some strings sounding. You need to stop these strings from ringing out when you play. This is where muting comes in. There are two ways to do this and you should use a combination of both. Drag a left hand finger behind the slide. With your picking hand palm cover any bass strings that you're not playing (for maximum muting use a thumpick or your thumb and use your fingers to mute strings)
Vibrato with a slide is very easy. Pretty much what you do is quickly shake the slide ever so slightly over the note (i.e. move it slightly up the fretboard and slightly down the fretboard very rapidly). This will slightly raise and lower the pitch. There is really no way to say how much you want to modulate the pitch, just experiment 'till you get what you like. Many players have an almost constant vibrato as it can help cover up less than perfect intonation and it sounds good.
Here are some more advanced techniques which you should attempt once you have the basics down:
01. Escape Notes.
Start by having your finger resting on the string behind the slide. Quickly slide up to a note and as soon as you reach that note pull up the slide. Your finger will prevent the note from ringing after you remove the slide. You should hear a very short, staccato note.
02. Grace Notes.
Grace notes on slide are very similar to what you do when you play standard. Basically what it is is you play one note and then very quickly play another note. The first note should not take up any time. You can do this through slides, hammer-ons and pull-offs, or bends when playing standard. With a slide this is only done throught slides. basically what you do is start above or below your desired note and quickly slide into it. Not much to it.
03. Fretting Behind The Slide.
This technique was pioneered by slide virtuoso Sonny Landreth (though I believe it was done before he was even born by delta blues guys like Robert Johnson). It's pretty self explanatory: when you have your slide down fret a note below the slide. The string will go down and (hopefully) will not be touched by the slide. For this to work you have to make sure that the slide does not touch the string. You can fret behind the slide with the slide on your finger but I'd definitely recommend having it on your pinky if you're gonna be using this technique a lot. The advantage to doing this is it gives you more complex tones (by mixing fretted and non-fretted notes) and just gives you more freedom (for example it allows you to play a minor chord in a major tuning.
Another great thing about slide is that you aren't limited to just playing the notes available in standard playing (A, C, E flat, F sharp etc). You can play the 'notes inside of notes' called microtones. To do this you simply place your slide in between two frets instead of right over one. However, don't think that you can get away with crappy intonation by just saying that you're using microtones.
05. Going Beyond The Fretboard.
Yet another great thing about slide guitar (there are just so many!! ) is that you don't need frets. That means that you can play beyond the fretboard for extra high notes. When you're doing this you have to be extra carful about your intonation because you have nothing to show you if you are in the right place. Another thing to remember is that you can't go beyond your pickup. So, if you're on your neck pup and you slide is in between the bridge and neck pup's and you're not hearing anything you'll know why. That is why I stay on my bridge pup while playing slide.
06. Behind The Slide Harmonics.
Here's a really cool thing you can do. What you do is pluck the strings behind the slide and you'll get a really unusual sound. It's kinda hard to describe. This works best at the 12th fret but also works at the 5th and 7th frets.
Playing slide (like all music) is all about listening. You can practice 10 hours a day for 20 years but if you don't listen to what others are doing you won't gert anywhere.
Here are some of my favourite slide albums and songs (which have great slide playing but are on an album which doesn't have much other slide playing) as well as others which I may not have heard yet but have been highly recommended and which I will be picking up eventually. The Allman Brother Band - Live At The Fillmore East (if you get any CD on this list this is the one to get. The original version is good but you should get the 2003 remaster as it contains several more slide tracks than the original).
Sonny Landreth - South of I - 10
Ry Cooder - Boomers Story (this is my favourite of his stuff but any Ry Cooder will be amazing including the Crossroads soundtrack and his work on the Rolling Stones' Let It Bleed and Sticky Fingers).
Eric Sardinas - Black Pearls
The Allman Brothers Band - Hittin' The Note (this is a recent album with Derek Trucks and Warren Haynes on guitar).
Derek Trucks - Derek Trucks
Fleetwood Mac - Peter Green's Fleetwood Mac (this is their first album back when they were a blues band and is not to be confused with the Stevie Nick/Lindsay Buckingham era crap).
Johnny Winter - Second Winter
Derek And The Dominos - Layla And Other Assorted Love Songs
Muddy Waters - His Best 1947 To 1955
Elmore James - The Sky Is Crying: The History Of Elmore James
Son House - The Original Delta Blues
Robert Johnson - The Complete Recordings
Charlie Patton - The Best Of
Irish Tour - Rory Gallagher
Songs: Joe Walsh - Rocky Mountain Way
Led Zeppelin - You Shook Me, In My Time Of Dying
I hope this has helped you get off to a good start playing slide. To continue your learning listen to some of the albums and songs mentioned on the previous section, learn some songs with slide playing, and check out some books on it or guitar magazines.