In order to have a lush and successful lawn, you need to complete several steps. You need to make sure you have proper irrigation of the seed bed, it needs to be fertilized properly and the temperature has to be in the range required for germination of your grass species. However, the most important thing to have a lush and successful lawn is to ensure you plant the correct amount of grass seed. Too little seed and you'll have a sparse lawn; too much grass seed and it'll choke itself out and you'll be left with a lawn prone to disease from weak seedlings. It is crucial yet easy to estimate grass seed amounts before you plant your lawn.
Measure the length and width of your yard. Multiply these two measurements together to get the square footage of your yard. So if your yard is 40 feet long by 60 feet wide, the square footage would be 2,400 square feet.
Look at the packaging of your grass seed. On the back the packaging will list how many pounds of seed are needed for each 1,000 square feet. Most grass falls between the range of five to eight pounds per 1,000 square feet.
Divide your square footage by 1,000 and then multiply by the pounds per square feet seeding rate on the packaging to figure out how many pounds of grass seed you need to seed your yard. So if you take 2,400 square feet (from the Step 1 example) and divide by 1,000, you end up with 2.4. Multiply 2.4 by eight pounds per 1,000 square feet and you end up with 19.2 pounds of total grass seed needed. You should be able to safely round down to 19 pounds and be fine.
Prepare your lawn for seeding and seed at the above calculated rate.