Lay down your seed either by hand or with a spreader for larger areas. Make sure you get enough down there so it covers the soil without piling the seeds on top of each other (figures A and B). Be careful not to spread seed to the flower beds or grass will start popping up everywhere! 

Cover the seeds with a thin 1/4 to 1/2 inch layer of either a "seed topper" or finely ground compost. This will keep birds from eating the seeds and it will hold the moisture in, which will result in better germination. 

Keep the area moist until your seed germinates and allow the grass to reach its maximum height, about 2-3 inches, before you mow. 

When it first grows in, it will be thin but it will get thicker each time you mow. Seeding will actually give you a stronger lawn in the long run but it does take longer than patching it up with sod. If you want instant results because you're hosting a party or just don't like waiting, your best bet is sod. 

Repairing Lawn with Sod 

You can find most sod in warm and cool season varieties and you can install sod at almost any time of the growing season. Here's how it's done. 

Remove the grass around the bare spot about 6 inches out. It helps to cut sections in rectangles (figures C and D) because that's the shape the sod comes in. 

Prepare the soil by removing any weeds or debris. If the soil is heavy clay or sand, add a little bit of compost. You want a nice garden bed so the sod will root. Level out the soil and tamp it down with a tamping tool. 

Cut pieces of sod to match the size of your bare spot. A soil knife works well for this (figure E).

Butt the edge of the sod against your existing grass line, laying it as tight as you can (figure F). Be careful not to stretch the sod though. 

Water regularly to keep your new sod moist. 

Tug on the sod after a week to see if it has grown in enough to attach itself to the soil. If it doesn't lift up when you tug on it (figure G) you can mow it. If it does come up, wait another week before pulling out the mower.

Watch your new lawn carefully. The edges of the sod strips are usually the first to dry out if you don't keep it moist.