Gotta agree with Spedzar here. A few things to help you out with improvisation:

1. Listen to the chord progression and [U]sing[/U] an improvised line to it. Find one you like, and then figure it out on the guitar. Why did that particular melody "work"? What's the underlying scale? This starts to connect your personal taste and sound to the music theory and your fingers without your technique and playing habits getting in the way.

2. Learn more chord / scale relationships and get them in your ears. Sing them and play them to expand your vocabulary when you improvise.

3. Play with a group or with recordings as often as you can to keep pushing yourself.