Well, now that we have a lawn chemical service, we regularly receive lawn-care newsletters about what we should be doing to our lawn to keep it at its optimal health and appearance.
One thing that is important early spring during the active growing season of the grass is to leave it at around 3 to 3 1/2 inches tall. That is because cutting it any shorter will 1. allow weeds to be able to take root and grow much easier because the seed has a shorter distance to dirt and 2. when cut too short your grass is being depleted of its nutrition.
If you have a problem with weeds often, think about the height of your grass when you mow it. If you have taller grass the weed will be competing for sun and nutrition, this competition is a good thing because far fewer weeds are going to actually survive long enough to be a problem.
Another thing important for lawn health is mowing with a sharp blade. If you have a dull mower blade it is going to be hacking at your grass to cut it rather than just going clear through each blade. When grass is hacked, it is sometimes just getting laid over rather than cut down.