If you haven’t already, it’s not too late to feed and seed your lawn. The most environmentally-friendly and effective way is to sprinkle existing grass with a light layer (½”) of compost. This will help put vital nutrients back into the soil without the risk of nitrogen runoff, which can happen with generic lawn fertilizers. The second best option is using a non-chemical lawn feed, such as Dr. Earth Super Natural Organic Fertilizer.
If you need to re-seed a bare patch, scratch up the soil with a stiff rake or hand-cultivator, sprinkle a generous amount of seed over the area, and top off with a light layer of compost. Keep the area moist by watering regularly with a sprinkler, watering can, or shower-setting on the hose nozzle. Stay off of it until the new grass is 3''-4'' high.
Avoid watering with heavy gushes, which can wash away the seed.
Don’t overfeed. Too much fertilizer can weaken a lawn's root development and can lead to a fungal issue.