You can be as free on the bass as you want, by keeping in mind that 
there are 4 degrees in playing to chord:   1 = Roots — 1
                                           2 = Chord notes — 1,3,5,7
                                           3 = Scale notes — 2,4,6
                                           4 = Remaining notes
Sooo you're only a halve tone off when you make a mistake. OKEY ;—)





A good way to learn how to solo is by starting to learn (Pentatonic 
Scales) FIRST!!
Pentatonic in Major = 1 2 3 5 6 8  — Don't play 4 and 7
Pentatonic in Minor = 1 3 4 5 7 8  — Don't play 2 and 8




If you want to expand you knowledge, then you should practise 
(Church Scales).
it sound stupid, but learn this and you can play/solo over most 
pop,rock music
Let me start by explaining how it works! (m=minor)
1 = Ionic      =    Major — 1  2  3  4  5  6  7  8 
2 = Doric      =    Minor — 1  2 m3  4  5  6 m7  8
3 = Phrygian   =    Minor — 1 m2 m3  4  5 m6 m7  8 
4 = Lydian     =    Major — 1  2  3 m4  5  6  7  8
5 = Mixolydian = Dominant — 1  2  3  4  5  6 m7  8
6 = Aolic = Naturel Minor — 1  2 m3  4  5 m6 m7  8
7 = Lockrian   =    Minor — 1 m2 m3  4 m5 m6 m7  8 
8 = same as 1 


So now you know how it works! Don't think you're there cos it's 
a long road.
FEW tips for soloing and Improvisation are..
— Use Dynamics!! play something softer and HARDER
— Use Hammer on's and Pull off's ,slides and Bend's etc.....
— Make a theme, that means when u are improvising and u play a sequence
  play that part a few times more in other modes for example.
— Start really lazy when starting to improvise, build up the 
tension! WHAAAAA
— And don't forget you're always a halve step from a good note!!!!!!!!!!

bye RTBM