1. You only have some years to develop speed, but a whole lifetime to get accurateThis is perhaps the most controversial piece of advice that you don't want to hear:
The earlier you start practicing for speed, the more likely you are to develop some great chops. I'm sorry to say this, but if you started "late," you can never get very fast. If you trusted the classic "play veeeeeeerry slow and then increase the metronome by five bpm everytime" you're very likely one of those players who complains about being slow 10 or 20 years after picking up a guitar for the first time. When we are young, our joints are flexible and very likely to learn new movements. Listen to recordings done by established shredders when they were teenagers. They were already very fast after some years of practicing. Guys such as Jason Becker, Paul Gilbert, Yngwie Malmsteen, John Petrucci, Steve Vai and Satriani were already fast enough as teens.
Thinking that you can still pick up a guitar in your late 20's or early 30's and develop a decent speed is wishful thinking. However, I think I might be able to help you develop a certain amount of speed. Read on.
2. Avoid linear picking patternsGo angular instead. Even the most challenging solos on guitar are objectively speaking easy once you get acquainted with angular picking patterns and melodies.
3. Pay attention to your postureHolding your guitar too high or too low will definitely have a detrimental influence upon your performance. If you truly want to know how fast and accurately you can play, place your guitar on your left thigh!
4. The thumb's positionClassical guitarists tend to economize movement and hand motions. For them, having their thumb stationed on the middle of the neck makes perfect sense. Thanks to the electric guitar's thinner neck, it is rather difficult to do that. A flexible thumb that rests somewhere above the middle of the back of the neck lends itself for better technicalities.
5. Most guitar solos are easyStop thinking there are things you can't play. This self-defeating attitude is probably the reason why you're stuck in a rut. In comparison to solo pieces written for other instruments, guitar solos are fairly easy. Whenever you think one solo by your favourite band or solo artist is difficult, try to play Paganini's 1st or 23rd caprice.
6. Don't forget "fast" is relativeTo some, 16th notes at 180 bpm are very fast. To others, 16th notes at 200 bpm are not a big deal. There is another guild to whom the fun starts at 230 or 240 bpm. Remember to set realistic goals, and don't forget about the aesthetic aspect of technique. 16ths at 240 bpm are sixteen (!) notes per second. After a certain speed, things start to sound pretty much annoying, so you either minimize the amount of speed, or avoid going to the limits altogether. Remember that fast stuff sounds less listenable on the guitar as on the piano.
7. Economize as much motion as possibleTo play fast you don't need to move a lot per se. Your right hand shouldn't look like you're jerking. Nor should the fingers of your left hand look like the fretboard is on fire.
8. Don't listen to what the pro's say unless you're paying them for adviceGuitar magazines are mostly filled to the brim with terrible advice on how to develop technique. Did you really think the pro's want everybody to be able to play astonishingly fast? It's like expecting alchemists to tell everyone how to make gold out of nothing.
9. The chromatic scale/exercise is NOT a speed exercise!The chromatic exercise doesn't require stretches that are particularly difficult. Unless you're a beginner, the classic 1-2-3-4 pattern will prove both easy and boring to you. Exercises that stretch your tendons=speed exercises. The chromatic scale is a great warm-up exercise, but you'll fail to develop true finger dexterity by practicing such a simple pattern for years. Don't be afraid to combine unusual intervals on the left hand with angular picking (mentioned above).
I hope these 9 recommendations are of some help to you. I invite you to take a look at my stuff on YouTube. Here's a video of me performing a classical piece I very much enjoy: