Don't Let Leaves Lie on Your Lawn
In Autumn leaves naturally fall off deciduous trees. If the leaves collect on lawns they can 'smother' lawn grasses; shading and squashing grass and encouraging damp conditions under the leaves where the disease may flourish.
So rake up those leaves regularly. Or you could blow them off or vacuum them up.
You do not have to rake up every leaf unless you want the look of a perfectly manicured lawn. If you just want to keep your grass healthy, a few leftover leaves won't hurt your lawn grass. If you plan on mowing at least one more time that autumn, the mower blade will simply chop up any remaining leaves and mulch them into the lawn.
Make the most of this bounty of organic matter and use the leaves in your compost. See How to Make the Best Compost. If you are going to consider mulching in the leaves read the article 'To Mulch or Not to Mulch?' for some advice.