clayie soil

I think that there is no magical answer.
Although clay soil isn't all bad, just heavy to work and can set like stone.

I can but suggest that you add almost anything and dig it in or let nature drag it in, worms do a great job but slowly. By anything I mean composted manure, compost from garden centres, chipped bark, sand.

It will take time and initially at least could be heavy digging anything in.

If you grow anything in pots, then once used tip the compost on as well.

I may have misunderstood. I thought that you were intending to rotovate the whole garden and plant a small patch of grass. The remainder being used for growing of something else such as veg and fruit.

If it is just the grass area that concerns you then as MOS says add something like sand, possibly some inexpensive compost, level and sow the grass seed. The sand and compost should help the grass seed take and give a fair surface for roots to develop.

thanks for the replys you have given me some very usefull info.