Here goes:
I've preached about the value of rhythm quite alot. Speed is based on the rhythmic groupings you're executing, i.e. 16th note, 8th note triplets, what not. i support the opinions of the folks here, get a metronome, build your rhythmic vocabulary. start slow. speed up. use sequences and exerps from solo passages you like. practice legato (non picked or lightly picked) or staccato (hard picked). if you have a harmonic and melodic vocabulary, you must work on your rhythmic vocabulary.
your set up is important. the basic set up for speed is a low action (i know this is disputable, but i'm covering the basics as a short cut) and 9 or 10 guage string sets. make sure your neck is a straight as a tack, your frets even. jumbo frets will help ease the fretting strain. i'm assuming that you've got them on your 'board (i'm relishing on the delights of small high frets, more dynamic for me. i wanna feel the wood)
the trick to speed? its in the conservation of energy, and the focus of it.
i'm sure you are familiar with the economy picking technique, where the most umber of notes are executed with the least movement and the lightest touch and effort. That is, what i consider the most popular technique featuring "conservation" and "focus". this deals with the right hand (given your a right-handed person who picks with the right)
how about the left (fretting hand)? it only follows logically that if the right hand has "economic" properties, the left hand should too. This is what i call (personally) economy fretting, involving hammering-on and/or pulling of with the least motion and most focus. study the left hand movement of the quickest and cleanest guitarists, and you will notice how effortless their lines are. that their fingers are "barely" hitting the frets but zoom across the strings, and every note stands out as like stars on a moonless night. its fretting kung fu, they are not "pushing" their finger tips on the board, but merely utilizing the needed "energy" to sound the notes. their fingers are discplined, performing only what is to be done, therefore, accurate and saving energy. that facility is borne out of practice.
how much of that energy is needed? here's how to find it and harness it:
1. line up all four fretting fingers on one string, say, the low E, covering frets 8, 9, 10 and 11.
2. do not fret these notes. let your fingers just touch the string.
3. raise your 3rd finger without raising the rest (i'm strict about this, JUST the the 3rd finger), to about 1cm.
4. allow it to drop and hit the string (10th fret) under it naturally.
5. repeat this for 1minute. make sure the other fingers do not disobey your command by lifting, they have to learn how to remain in file.
6. move on to the pink, after a minute again, to the 1st finger, then the second.
thats it. focus on its energy with all your zen. as you practice, you will find your touch gather more strength and with less effort, and that your fingers will be sounding the notes with the least movement.
good luck, grasshopper... practice makes more practice...