Dissuade people from parking on your grass. It may seem simplistic, but the most direct and effective way to avoid getting tire ruts in the grass is by keeping people from parking in the grass. There are a few ways you can approach this. If it's your own family members, tell them directly to park in the driveway and not on the grass. Install a "no parking" sign if it's an area where neighbors are parking. As an alternative, place boulders or plant a border shrub such as monkey grass in order to dissuade people from parking in the area.
Check the drainage in the area where the ruts appear the most, especially if it is along the street next to your drainage ditch or gutter. Although people parking on your grass can sometimes cause ruts, if the area is dry, the ruts shouldn't be bad. Deep ruts or soggy ground may be an indicator of a larger problem such as poor drainage or a burst underground water pipe. If you suspect the latter, notify a plumber or the water company.
Clean out ditches or gutters if that is where the ruts are appearing the most. Specifically, use a rake or hoe to clear out the drainpipe that runs under your driveway. If necessary, dig your ditch deeper with a hand shovel.
Pour sand in the areas where the ruts seem to be appearing the most, or in areas that may seem soggier than the rest of your yard. The amount of sand you need will vary based on the area that needs to be covered.