Theres a saying we use in the military. It goes "Slow is smooth, smooth is fast". What ever you work on, make sure you have it down slow first as well as smooth. There are some songs Ive never practiced fast, but because Ive played them countless times, I can easily take them faster. Confidence is also a factor in speed believe it or not. You can have wicked speed and still be sloppy. Alot of players dont get things down before they start trying to blaze super Jaco style. Whether it be scales, dex. exercises, riffs, etc., take the time to get it down and tight. Ive read where Thelonious Monk practiced one song for two hours straight. I havent been that far, but Ive taken some dexterity exercises or lines and worked just one for 15-30 mins (if you watch the clock, that is a VERY long time for one thing). I would run it very slow for about 5 min, then depending on how tight I have it, I would increase the metronome by 10-15 clicks then go another 5 minutes and so on.