Dampening the strings, much in the style of Al DiMeola and Eddie Van Halen, is a good way to develop smooth speed. When you dampen the strings you can't get away with anything. It forces you to be articulate because you can't depend on sustain to carry you. It's like playing drums on a rubber practice pad instead of on real drums. You have none of the advantages of the sound. You're naked and right out there. More to the point, when you play a fast run it can sometimes come out cleaner if you dampen the strings. It's also very stylish. Say you have a seven note run of 16th notes, just dampen the first six notes and end on one sustained note. I dampen or mute the strings by lightly resting my right palm on them.
I also recommend to guitarists that you not anchor your picking hand on the bridge or pick guard. I know that a lot of guitar players with terrific chops play that style, but I think it's always better to have the freedom of not anchoring your hand. I practice cross picking from the forearm, so it's not so much just wrist and fingers. Make your forearm your anchor. It frees you so you don't always have to play near the bridge. If you want to play in a smooth style with long sustaining notes you can play up nearer the neck and get fewer harmonics and more of a liquid tone. Enough talk, let's do a muting exercise that sounds cool. It may even remind you of said Al DiMeola.
This is in D major and we'll be raising the tonic, third and fifth by one fret (half step). Start with D# to D on the 11th to 10th fret of the high E string with your second and first fingers respectively. Then it's your pinky on the B string 13th fret, second finger on the B string 1lth fret and first finger on the B string 10th fret. The G string plays two notes: the third finger on the 12th fret and the second finger on the 11th fret.
The D string has notes fretted on the 13th, 12th and 10th frets played by the pinky, third and first fingers respectively. Repeat the exact fingerings on the A string playing the notes A#, A and G. Then the first finger slides down one more fret to the F# on the 9th fret of the A string. The last two notes are D# on the low E 11th fret, using your third finger, and the D note on the 10th fret of this same string played by your second finger. Good chords to play under this run are D and C minor. Remember to use alternate picking and start slow.