I saw this post and just wanted to add that I have had the same series recommended to me by TSax on another thread. I now see that if you want to begin improvising straight away, the Guest Spot books are of limited value, particularly as they don't contain chord symbols. However, I do think they are a good introduction to the music and it is great fun playing along with the backing tracks!
I've recently bought the ABRSM Grade 1 level Jazz Clarinet and intend to look at the Aebersold series next. Although my classical playing is around Grade 5 - 6 standard, improvisation is not something I've done up to now and I suspect that I'm going to have to work at it! Hopefully, I can have some fun doing so!