1. Aerate: this means removing plugs of dirt from the lawn so that air, water and nutrients can reach the roots. Soil can become hard and compacted over time and by aerating regularly (spring and fall) you will loosen up the soil and feed the roots. You can rent an aerator from a rental company or hire a landscape company to do this for you.
2. Overseed: keep your lawn thick and healthy by regularly adding grass seed in the early spring and late fall. You can mix the seed with compost or top-dress with triple mix soil to help improve the soil and add nutrients at the same time. If you need to pluck weeds, add some grass seed to any bare areas.
3. Mow smarter: Reduce the growth of weeds by cutting your grass less often. Keeping the lawn between 6 and 8 cm (2 1/2 to 3 inches) high blocks out the light weeds need to germinate. Consider a push mower. Push mowers cut grass blades cleanly, making it healthier and more pest resistant. They’re also better for you and the environment.
4. Feed it naturally: leave your lawn clippings on the lawn after you mow – they make an ideal (and free) fertilizer. As they break down they release nitrogen into the soil. Use compost or all-organic fertilizer in the fall to feed the roots of your lawn.
5. Apply natural fertilizer. Don’t over-fertilize and follow label directions carefully. It is best to use organic products such as finished compost and grass clippings that can be applied throughout the growing season. Slow release organic products such as well-aged manure and seaweed are also good fertilizers. It is recommended to apply these fertilizers in late summer or the early fall but they can also be used in the early spring. Make sure you evenly apply lawn fertilizers to achieve a uniform green lawn.
6. Make sure your fertilization includes the main nutrients that work to keep it attractive and healthy. These nutrients are: Nitrogen to maintain a dark green color, thick turf and a strong lead and blade and Potassium to help keep the plant strong and resistant to wear, drought and cold winters.
7. While phosphorus is an important nutrient for grass growth, many lawns have adequate amounts of phosphorus in their soil, so test your soil before buying fertilizer containing phosphorus. Visit your local garden centre to purchase a soil testing kit. To learn about how phosphorus affects our water systems, please see “Healthy Lawn, Healthy Lake”. For more information on soil testing, call OMAFRA at 1-877-424-1300.
8. To determine the amount of nutrients needed by your lawn, test the soil.
9. Water wisely: your lawn needs only 2.5 cm (1 inch) of water a week. Water deeply and infrequently to promote deep roots. Early morning is best when more water will be absorbed than during the heat of day. Too much water starves the soil of oxygen and invites disease. Pay attention to when rain is expected in your area and don’t water during droughts. Your lawn can go dormant and will be green again as soon as the fall rains come.
10. Rake: Rake in the early spring to remove the dead grass, or thatch, that has built up. This will increase water absorption on your lawn. It is better to rake in late spring or early summer when the grass is not too spongy and there is no danger of damaging roots.
11. Pluck weeds by hand: spring is a good time to hand-pull weeds like dandelions while the soil is damp and their roots are not so long and tough. Get a weeding tool (fork or claw designs work well) and the job will be faster and easier. Then add some compost and grass seed on the spots you’ve weeded.
12. Tips for pulling weeds: It is much easier to pull out weeds when the ground is sufficiently moist like after a rainfall. Aim to dig out the entire root of dandelions and perennial weeds with the help of a weeding tool. Be on the lookout for weeds with tiny flowers. Try to get rid of weeds before their flowers fall off and seeds form.
13. Select grass varieties to suit soil and growing conditions: There are some new varieties of grass seeds available that are better suited for our Ontario summers. Choose hardy grasses that don’t require a lot of care and are specific for your property, either shady or sunny locations.
14. Use Corn Gluten Meal: Corn Gluten Meal is a great way to keep lawn weeds at bay. Available at most garden centres, it works to inhibit growth during seed germination. Apply in the early spring and wait at least 4 weeks before overseeding.
15. Test Your Soil: Problem soil may have a pH imbalance. Ask your garden centre where you can purchase a soil test kit to check. Hiring a lawn care service is also an option.

Source: http://www.ene.gov.on.ca/environment/en/residents/tips/?categoryId=10