Answer: I suggest that you loosen the soil in the dead patches so fertilizer and seed will be more effective, but the dead grass can actually provide some protection against erosion and birds (who love grass seed). Loosen soil to a depth of 5-6", mix in the fertilizer, and then sow the seed. Tamp the area gently to firm the seed in place, and then cover lightly with the dead grass and some straw.
If the grass is dead as the result of dog urine, then the soil needs to be flushed of the built-up salts that killed the grass, and will prevent the success of new grass. Flush the area several times before planting, allowing the soil to drain well after each flushing. If disease or pests caused the problem, then you should remove the dead turf, as it may be a reservoir for future problems. Best of luck!
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