The ultimate technique for improving your soloing: listening.

There are a million bedroom shredders out there who go balls-to-the-wall for speed and totally forget that there is a melodic component to music. There are some non-technical guitarists out there who's skills I envy because they have an ear that I simply don't.

If you're looking for speed, focus instead on economy of motion and comfort. Speed will come with time as small, economic motions become muscle memory.
Dont just learn speed. To many players learn to play fast with out learning how to use it.

To play fast decently, you have to know what do play fast.

I personally saying don't worry about the speed unless you know how to solo well over a 12 bar blues.

But, to answer your question, you want really good, clean alternate picking, legato (hammer ons, pulls off, tapping, bending, and vibrato! don't miss out that vibrato.
As said before, don't go just for the speed.

If you want to play fast solos, go for players that play fast and with flavor.
A good example of this is Marty friedman, check out what he did in megadeth.

But yeah, if you want to play fast you have to practice slow and get everything perfect and BE RELAXED. Otherwise you wont get faster at all, or atleast not for a long time.
I actually just had a good idea.

Guitar world done a series called solo strateies which is on their websites. It analysis guitar players soloing styles.

It goes over what scale, arpeggios, triads, modes etc that they use aswell as the technique they use and their phrasing. It then puts it all together to show you how it is all used in a solo.

Guitarists they have done iclude Jimmy Page, Randy Rhoads and Jimi Hendrix. It is all very useful stuff.

But makes sure as well as learning the licks and stuff that they give you, learn the scales to, or they wont make sense and you wont be able to use them properly.

Pick a fast-ish solo you like. Slow it down to half it's speed. Learn it at that speed for a few weeks. Then, you'll find it much easier to build up speed with it because you should know it off by heart by then.
Well, speed is practice, but the best way to improve your solos is to improve your reletive pitch. if you practice guitar and pitch, then suddenly, on day, you will be throwin' out solos from your mind and your fingers will know where to go without thinking about it. THATS when your really playing
cool just practice? if you just want to learn how to play faster thats the easiest thing ever.

learning how to play better and write solos...now you're in a different ball park.

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