There are few things that hold young violinists back as much as speed does. A very easy piece can become unplayable at a fast speed.
http://www.youtube.com/watch?v=j-Gp3hTVeq8
The youtube clip of Ben Chan playing and pushing up the speed of the Bach Presto (from the Sonatas & Partitas) demonstrates how you go about it.
There are other ways and means of course; but the metronome is the most important.
But in effect, you need to know your piece pretty well. Don’t try pushing the speed limit with a piece you’re still learning. This means: Practice!!!
Eventually it also means letting go and allowing yourself to play at that speed. When you know the piece well, playing fast shouldn’t feel like pushing, it should feel like flying.
Enjoy your speed! 😉
(A tip: Ben Chan has a lot of good YouTube vids out.)
Violin Tricks 