There are probably areas of bare spots and dead grass. If the summer was harsh, it might even be in a lot worse shape.
Reseed these damaged areas in the fall after the lawn is aerated and dethatched. Using high-quality seed will make a big difference.
Be sure not to overseed too late in the fall, or the new grass won’t survive the winter. The warmer fall soil will encourage quick germination. And the cooler air temperatures will make sure the young grass doesn’t develop heat stress.
A lawn spreader works well to seed larger areas; use a hand spreader for smaller ones.
Tamp down the areas of new seeding to help the seed stay in place for germination. For these seeds to germinate, they will need to touch the soil.
You can cover newly seeded areas with straw or leaf compost.