Luca said: @Flint
Sorry for asking, but why is regular mowing so important beyond just making it look nice?
That’s not a silly question. Regular mowing with a sharp blade lessens the stress on the plants and encourages side growth, which helps fill in the thin areas.
Fertilize, water, mow. See what happens over the next couple of months, then adjust for next year (check for any weeds, diseases, or pests that show up, etc.). Consider using pre-emergent next year and do a soil test later this year if needed.
That’s a lot of thatch. For a quick fix, get a dethatcher (you can buy an electric one, rent, or if your space is under 1000 square feet and you’re fit, get a manual one). First mow low, dethatch, mow again to pick up all the thatch, overseed, and use the back of a rake to mix the seeds into the soil. If you want to save money, it’s good to get some topsoil and spread it before seeding and then rake it in. Water at least twice a day. You should water every time the top layer dries out, so around 3-5 times a day. This is just to start and will get you going. Once you get the hang of lawn care, you can do more like core aeration or a full renovation.
You could also spray a product before mowing. If you plan on doing lawn care for a while, investing in good equipment is a big deal. A backpack sprayer makes a huge difference. A good broadcast spreader also helps a lot.