No simple answer to this, other than the obvious …practice.
The main thing is to find the problem areas and work on those. It also depends on what your goals are – for example, shredding / alternate picking 16th notes at 180BPM plus, or just typical “fast” blues / rock licks, legato etc. All different techniques. I’m not a shredder so can’t help much with that but for rock / blues etc I’m hoping to get some speed building stuff on the site quite soon.
Also, check out Troy Gray’s Cracking the code – it digs deep into the subject and is a great resource.
Lee Answered question