What's wrong with it - poor grass, bare patches, weeds or all three? Is your ground in sun or shade, is it wet, normal or dry soil, do you have moss? Does it get a lot of wear?

When was the last time you fed it, and with what? How often and how low do you mow it?

Thanks for your comments. The grass is poor with bald patches. The soil beneath is very stoney but it has good drainage being on a slope. I last treated it with weed and feed about April time

Just wondering if the ground was well cultivated before the grass went down. Sounds as though it might have been laid at a new build without removing enough builders rubble - iff some of the stones are large and near the surface that can cause bare patches as the ground will dry out there more quickly than elsewhere.You didn't say whether you had laid the lawn recently of inherited when you moved.
Perhaps it might help if you thoroughly spike it and brush some good compost into the spike holes. Other than that I can't think of anything else except an autumn feed, without digging it up, improving the ground and starting again.

There are pluses and minuses to a slope. You don't have to worry about the lawn turning into a marsh at snow melt, but in summer, it makes it harder for water and nutrients to penetrate to the grass roots. Also, it helps to know what the slope is made of: if bedrock is near the surface, it will be a hardscrabble life for your lawn; if there are large rocks embedded in the soil, they would account for at least some of the bare spots. A few test holes might be in order. If the soil and subsoil is decent--around the little rocks--all that may be necessary is to increase the ability of the soil to absorb the water that falls on it. The best way to do that is organic matter. I would add about a cm of compost every year, though others will have a better idea of the best time to do that in your climate.