The short answer
Scratch the surface up, sow seed mixed with compost, firm it down and keep it damp. Spring and early autumn work; midsummer usually does not.
- Choose spring or early autumn, when the soil is warm and moisture is reliable.
- Rake the patch vigorously to break the surface and remove the dead material.
- Mix grass seed with a little compost or topsoil and spread it over.
- Firm it gently with the back of a rake or by treading, so the seed contacts soil.
- Keep it damp for two to three weeks. This is the part that decides whether it works.
- Keep off it until the new grass has been cut twice.
What will ruin it
Find out why the patch is bare before you reseed. A dog's regular spot, a buried slab, a drainage problem or heavy foot traffic will kill the new seed exactly as it killed the old grass.
Why it works
Grass seed needs soil contact, warmth and consistent moisture to germinate. Scattering seed on hard bare ground in July fails on all three, which is why most reseeding attempts fail.
Tipking is general household information, not professional advice. Test anything on a hidden patch first. Full disclaimer.