Riff A (verse)

G|---------------------------------------------------------|
D|---------------------------------------------------------|
A|---------------------------------------------------------|
E|--5-5-3-5-5-0-5-0-3-5--repeats--------Then---------------|

Riff B (chorus)

G|---------------------------------------------------------|
D|---------------------------------------------------------|
A|--33-303-0-30-30-----------------------------------------|
E|------------------33-0303-034-Back to riff on A----------|

that's basically it,there's some variation in the pattern

from verse to verse but this is the basic structure.