[JKT]

Having never read any GTD book at all, and assuming I haven't managed to adopt the one true way™ method through serendipitous chance, OmniFocus works very well for my own home-built methodology of getting things done. The only trick to staying productive, I would say, would be to get your contexts nailed as early as possible. However, they don't have to be perfect and can and will evolve with time until you get that 'perfect set'.

The only other tip, though non-essential - get an iPhone for OmniFocus if you don't have one already.