Answer: I would suggest you start out by running some basic soil tests to check the fertility and soil pH. The test results will tell you how much fertilizer you should use and whether or not lime would be helpful. Lime is used to adjust the pH, the correct pH helps the grass use the fertilizer. There is no other way to tell without testing, and you should test every few years.
Next, consider topdressing with good quality compost and doing some core aeration. Core aeration pulls up plugs, it does not just spike the soil. This will help add organic matter and allow air and water to enter the soil better.
Then you could overseed. September is the actually the best time to seed lawn grasses -- assuming the drought stops by then.
Your local Penn State county extension should be able to help you with the soil testing and interpreting the results, they will also be familiar with the best lawn grass varieties for your local area soil.
I hope this helps!
Q&A Library Searching Tips