I am a big puss, and rarely (if ever) use the hook grip on anything.
I read once that one of the Magnusses (there's like 14 of them in WSM competitions) suggests flexing your wrists inwards a bit, to incorporate the forearms a bit more in gripping the handles.
The best tip I ever read on the topic was from Mike Robertson, I believe. He said that when doing any weighted carry (farmer's walk, wheelbarrow, whatever), pull your shoulderblades back and down. It definitely keeps your posture in tact, and distributes the load across your shoulder girdle, rather than straight down your arms.