Evan,
Are you doing your backyard or prepping a fairway for the U.S. Open?
Rototill to a depth of 6 inches, it will take a few times over to make it right. It's a good time to till in any fertilizers, lime or soil amendments that may be helpful.
Soft is good. It means you've aerated the soil and grass likes airy soil. If it's too much so, rent an old fashioned roller and roll it down, or, if you want to get hi-tech, rent one of those little Wacker-Packer vibrating, walk-behind compactors. Even after running over it with that you'll still be way ahead in the aeration game.
After seeding, the most important thing is to keep the surface wet until you have germination and you see at least two leaves on the plant.