Our front-yard had a few patches where there wasn't much grass. The yard closest to the house doesn't get a lot of direct sunlight.
I bought a "lawn repair kit", which is a mixture of grass seeds and fertilizer, mixed through paper pulp. It looks a little weird, but now a week later there are tiny sprouts of grass showing, so it seems to work.
It is nice to work on the yard, and take care of things like this.