To extend on the excellent advice already given, if you have one position totally down, look at extensions of it. On the B and E strings, go up to the next position. On the E and A strings, drop to the previous position. Then fill in the middle.

I'll just reiterate how incredible the blues course is here to help you learn improvistion. Anders has some great advice too if you read through his section of the forum. It's a common stumbling block and I came here looking to get past it...which I did.

Learn how to imrpovise slow. You can create some really cool solos without speed. Speed is just ONE dynamic you can use for creating a solo. Anders is a master of this...he can certainly play fast, but he'll show you that you don't always have to.