It is important to learn about the scales and modes and arpeggios, but it is very easy to get locked inside your own practice patterns. When you finally have got a technically challenging lick nailed it is very tempting to use this lick and slight variations of it over and over again, because you can make it sound great. One may become amazed by one's own technique and this is of great danger for the creative soloist.....

What you need to do besides rehearsing the scales etc. is to just play with one intent: To make it sound good! It sounds banal, but it is so important. Take a simple melody that pops into your head and try playing it. When this process becomes faster and more automatic as time passes you are very close to beeing a scilled improvisator.

And then you realize that you are playing scales and arpeggios, but you're playing them with creativety and with empasis on phrasing and melodic patterns.....things that make a good technical guitarist a great musician. Be aware of what you play, and, like someone on the list said, take chances and practice covering your mistakes.

Be creative!