First I recommend doing a soil test if you haven't done one in several years. It will tell you your soil type, pH, fertility and more - helping you to properly fertilize your lawn and have a stronger, denser turf to better resist disease and insect infestation. It only costs $25 and they will provide you with a fertilizer recommendation in addition to the analysis of your soil sample. Knowing the condition of your soil is the starting point to establishing & maintaining a good healthy lawn. More info here:Don't Guess-Soil Test-MSU and MSU Home Soil Test-self mailer

I suspect you may have an insect pest problem (Japanese Beetle or ?) so I'm attaching links to insect pest info for you to check out:

MSU Turf Insects

Turfgrass Insects-Purdue

Turfgrass Insects II-Purdue

Turf Diseases & Pests-PSU

How Do I Treat for Grubs in My Lawn-UNH

I caution cutting the lawn short as short turf blades yield short turf roots.  Read this: Why Mow High-MSU

Since you have sandy soil, adding organic material will help feed your lawn and retain moisture longer (less watering).  I'd consider adding compost (via a spreader) and mulching leaves into the lawn each fall to add organic content.  

Using Composts to Improve Turf Performance-PSU

Mulch Leaves into Lawn-MSU

Here are some general lawn care guidelines to help you best care for your lawn: 

Home Lawns | MSU Extension

Steps to an attractive lawn-Cornell

Benefits of Slow Release Lawn Fertilizers-MSU