The previous answer is good advice for establishing a lawn, but if you can't or don't want to start completely from scratch, then start by getting weeds under control. YOu can use a weed and feed (or a broadleaf weed control spray -- same stuff) this fall to take out dandelions and other broadleaf weeds. Then next spring, use a weed preventer to stop crabgrass and other annual weeds. Once you get the weeds under control, you will have a better sense of your lawn's condition. If there's not much grass, you may wish to overseed (which can be as simple as scattering seed around and scratching it in with a rake) to thicken up the lawn. However, many lawns will fill in gradually on their own. You dont' say what sort of lawn you have, so I can't be more specific about that.
Hi, Well the best way to have a good lawn is to have good soil. You don't say what your yard is like in terms of soil, drainage or exposure, but in general, the best way to have a good lawn is to start by improving your existing soil with organic matter such as compost, rotted manure, leaf mold, etc. Then, rake the area smooth and seed, keeping the seed bed moist until the seeds germinate. It also helps to use a quality seed mixture because many cheap seed mixes contain weed seeds. Once the grass is up and growing, mow to a height of 3 inches. If you want a perfect lawn, you'll need to use a weed and feed product at regular intervals.