I agree with following Eric Bolvin's site and his online lessons. However, like you, I am working on improvisation; and another way is to get the S.P.I.T book by Dr. Mark and Jane Shellhammer. The S = scales; P = Patterns; I = Inversions; and T = Triads. With this book, all you have to know is the key whatever song you are playing is in. Then you find the key in the chords in the book, i.e. key of C and find chord of Cmaj or Cminor. Then pull out that page (book is loose leaf binder). Each page had the scales, the patterns WWHWWH, and the Inversions and Triads. You play each in quarter notes, eighth notes or triplets or a combination of all three.
What it comes down to, is the fact that all the chords must be memorized eventually. My problem, as I get older is the memory. But, even then, if you have the sheet in front of you, you can most likely find something to play.