...perpendicular to the roof trusses. I found that the first several rows were very difficult (particularly with my low 5/12 roof pitch), but once I got them out of the way, the rolls of insulation would clear the top truss cords and would virtually unroll themselves. The only pain was cutting/working around the truss "webbing" (the diagonal framing members within the plane of each truss) where they interfered with the rolls of insulation.

I didn't take the time to install baffles between the top cord of each roof truss to insure airflow between the roof sheathing and insulation, so I just made sure to keep the first roll of new insulation back far enough from the eave that it just barely touched the bottom edge of the top truss cord. This left approximately 12" of ceiling below exposed (except for the ~4" of existing, compacted blown-in insulation that was already there), but insured that I still have airflow from the eaves to the ridge vent.

Having some small pieces of plywood that you can slide around and use to kneel on as you work will be a tremendous help. Just make sure they are wide enough to span at least one truss bay, and sized appropriately so that you can manipulate them easily and also not have sizeable area cantilevered past a truss where you could accidentally kneel and flip the plywood. You don't want to fall through the ceiling below. Also, wear a dust mask, or better yet, a respirator.

Finally, the best way to get started is to do as Hurley did, and DonHo suggested - just get started. Once you displace the attic stuff to make room to work, you'll be motivated to finish as soon as possible so you can put it all back in the attic (hopefully after you make yourself purge some junk).