This is pretty old, so you might have seen it before, but while perusing YouTube earlier I came across a pretty lenghty
video interview/guitar lesson featuring Adrian Smith.
He doesn't sit down and discuss theory or anything like that, but he shares a few techniques and shows a few of the detuned Maiden riffs he plays these days.
Good stuff...even though I'm kinda irate that he can take a Squier Tele and a practice amp and sound heavier than I do with an SG and a Marshall stack. :P