This is the main riff for the song. It's played over the 12 bar blues chord progression. 
As usual with Jack Bruce he improvises loads on the solo. Ive written a few of his fills 
on my 'Deserted Cities of the Heart' Bass tab.

This is how it goes.

g|————————————————————|
d|—————2—3————————————| x 4
a|—3—4—————3434———————|
e|——————————————3—4———|

g|—————2—3————————————|
d|—3—4—————3434———————| x 2
a|——————————————3—4———|
e|————————————————————|

g|————————————————————|
d|—————2—3————————————| x 2
a|—3—4—————3434———————|
e|——————————————3—4———|

g|————————————————————|
d|—6—6—4——————————————| improvises here a lot.
a|———————6h5h4————————| x 1
e|—————————————6——————|

g|————————————————————|
d|—4—4—2——————————————| improvises here too
a|———————4h3h2————————| x 1
e|—————————————4h3h2——|

g|————————————————————|
d|—————2—3————————————| x 2
a|—3—4—————3434———————|
e|——————————————3—4———|

Thats it! If youre confident enough with 12 bar blues you can just let out fill after fill 
on the guitar solo, if youre not so confident just play the riff in the order above until 
youre confident enough to mess around. Enjoy!