Tall fescue is the grass often recommended as being well suited for the climate and soils of Maryland's diverse terrain. Other grass cultivars are also available. The University of Maryland Cooperative Extension Service recommends publication AM-77: "Turfgrass Cultivar Recommendations for Maryland" as a guide for grass seed selection.
You'll need to properly prepare the soil for success of any grass seed you plant. Remove existing grass and weeds and clear soil of any debris. If it's been awhile since you planted on your lawn, test the soil to make sure it will support a new lawn. Add soil nutrients before planting if necessary.
Grass seed planted during spring months lacks a good foundation before the arrival of summer heat or drought conditions. Planting during the end of summer or early in the fall gives seed time to establish and winter over prior to the onslaught of Maryland's somewhat unpredictable summer weather.