alot of metal makes use of the Phrygian Mode. If you don't know what it is there are alot of places you can look it up. Here's an example of the pattern though


e|-------------------------------|
B|-------------------------------|
G|------------------------7--9--|
D|------------7---9--10---5--7--|
A|-7--8--10--5---7---8----------|
E|-5--6---8---------------------|

fool around with it and see what you can come up with.

leedogg's version of Smoke on the Water is the most accurate if you want to play it the way Ritchie Blackmore plays it, otherwise it doesn't really matter, maybe you're looking to play an ultra heavy version of Smoke.