The picking hand
(ie the right hand for right-handed people)
• When using the plectrum, don't make a fist. Have the 2nd. 3rd and 4th fingers loose by the index finger. Pick several notes on the top string and have the little finger touching the scratch-plate or soundboard.
• Make the movement from the wrist, not the elbow (don't copy Pete Townsend of The Who).

The fretting hand
(ie the left hand for right-handed people)
• The edge of the palm below the little finger must not touch the neck.
• Apart from for barre chords, all the fingers are curled, not straight.
• Fret the strings just behind the fret, otherwise you risk a buzz.
• Keep the fingers close to the strings. (There is a great simple exercise my guitar teacher gave me to develop this.)

Minimum movement
Always use as little body movement as possible.

The plectrum
• Don't pick the string 'flat on'. Approach the string at a 10 degree angle.
• A heavy pick gives a fat sound, a thin pick gives a thin sound. On light guage strings (.009 inch for top E) I use a medium grade (0.7mm) pick.

How to sit
Don't sit on a sofa! Sit on an upright chair, with a back rest. Keep your back pretty straight, don't push your neck too far forward, and have the two shoulders more or less level with each other. Keep your shoulders relaxed. Get a music stand, so you are not peering down at the music. Use a strap for electric guitar, and have the nut about level with the shoulder. I am in a minority here, but if you have a Strat-style guitar, I recommend a strap button placed on the backplate behind the neck, not on the upper horn. This keeps the left-hand wrist at a less acute angle, preventing strains and maximising access to all parts of the neck.

How to stand
Stand up straight, and have the upper body feel exactly the same as it feels when you are sat down.

Practice
You may have heard this one before, but it's good advice: a little and often is better than one big dollop. So make sure you practice for a minimum of 60 minutes each day (or at least, 6 days per week), otherwise you will always feel you are going uphill.

Sound
The biggest lesson I got from my guitar teacher, was to listen to the sound I was making. Choice of amps, strings, pickups etc is important, but the first thing you have to do is listen to sound you create with your own fingers as the string vibrates. This means checking whether it's too soft or loud, whether it's scratchy, or apologetic etc. You have to pay close attention to all of the physical aspects of technique to get sounds that are even in volume, rhythm and timbre. To listen to your sound with this critical ear it's necessary to slow things down - you won't hear the glitches and wobbles if you only ever play fast.

Bite-size chunks
When you see what the possibilities are on the guitar it's tempting to try to learn eveything all at once, eg trying to learn 5 scales all in one week. If you do this you'll only get confused, or else trip up. I think the only option is to take the 'steady as you go' approach, going little by little, building the foundation of a sound technique.

Too much technique?
I think there's no such thing as having too much technical facility: it's the lack of technique that gets in the way of making the music you love.