Q     E E E E E  W                Q     E E E E E  W
----------------|----------------|----------------|----------------|
------------8-8-|10b11-----------|------------8-8-|10b11-----------|
----------8-----|----------------|----------8-----|----------------|
6-----8-9-------|----------------|6-----8-9-------|----------------|

Q     E E E E E  W                Q     E E E E E  W                              
------------8-8-|12--------------|----------------|----------------|
----------8-----|----------------|------------8-8-|10b11-----------|
6-----9-10------|----------------|----------8-----|----------------|
----------------|----------------|6-----8-9-------|----------------|

Q     E E E E E  W                Q     E E E E E  W
----------------|----------------|------------8-8-|12--------------|
------------8-8-|10b11-----------|----------8-----|----------------|
----------8-----|----------------|6-----9-10------|----------------|
6-----8-9-------|----------------|----------------|----------------|

Q     E E E E E  W                Q     E E E E E  W
----------------|----------------|----------------|----------------|
----------6-8-8-|----------------|------------8-8-|10b11-----------|
----------------|8---------------|----------8-----|----------------|
6-----8-9-------|----------------|6-----8-9-------|----------------|

This is the basic riff and after that there are some minor variations 
where the bass player improvises but once you get the hang of this 
standard riff you should be comfortable improvising yourself.