[BackingTrack] Bossanova 1-6-2-5 in Bb major 

I sometimes wish I could play saxophone!

Best advice I can give is to learn to "play the changes", which basically means playing phrases that target notes of the underlying chord. In Bb, a I-vi-ii-V is Bbmaj7 | Gm7 | Cm7 | F7. I also hear a b9 on the F7 pretty frequently, enough to consider the chord F7(b9). Bbmaj7 - Bb D F A Gm7 - G Bb D F Cm7 - C Eb G Bb F7(b9) - F A C Eb Gb So those are the notes you should be targeting. As you progress further you could experiment with implying extensions even if the chord isn't playing them (such as playing an A over Gm7 to imply a Gm9) but IMO it's probably best and most straightforward to stick to the base triads to really get a feel for the concept before you start adding in 7ths (the targeting of which will be a very good source of a jazzy sound) and higher extensions. Personally, during improvisation I would think of the whole thing in Bb major, target chord tones where appropriate, and account for "out-of-key" notes where appropriate, such as the Gb in F7(b9). It's not a substitution for learning to play the changes, but as a hot tip: try D minor pentatonic. You might be surprised at the results as playing D minor pentatonic over a Bb chord implies a Bbmaj13. It will be pretty useful over the Gm7 too but maybe a bit less useful over the F7(b9) as D minor pentatonic contains G and F7(b9) contains Gb so these notes will clash. It may not be an optimal approach to the Cm7 either since the color tones of the chord, the third and the seventh (Eb and Bb respectively for Cm7), are not found in D minor pentatonic at all. Not to say it couldn't work, but wanted to illustrate why this approach is really just one hot tip and isn't an effective substitute for actually learning to play the changes. Hope this helps! Good luck and happy playing!

play the pentatonic scale in the key. Also try to play the root note of the chords at the beginning to be aware of the notes you have to play. Second step, when you play the pentatonic, try to add the 4th and the 7th note of the scale, they are more "jazz" sounding since they are a little bit dissonant. Third step, Try to add chromatism. This means playing "wrong notes", every wrong note is 1 fret or half step away from a good note. So try to make the next note sound good, It adds tension and release. For exemple, you can play a dissonant note on the V chord, and on the I, add a consonant note