Q.Tilling and topsoiling
I have a portion of garden which I intend to sow to lawn. The soil is very poor, so I have some composted topsoil I intend to add. Is it better to spread the topsoil before tilling, or till first and then topsoil, or does it make any difference?

Certified GKH Gardening Expert
It's best to spread the composted topsoil before tilling, in order to incorporate it with the native soil.
After tilling, rake it smooth and water heavily to settle, then when dried out a little so its not muddy wet, rake again to prepare your seed bed. After seeding and lightly raking in the seeds, apply an even top dressing of fine textured compost about a quarter inch to half inch thick or straw over the seed to retain soil moisture so the seeds don't dry out as they germinate. Water to keep the top dressing and seed bed moist.
https://www.gardeningknowhow.com/lawn-care/lgen/lawn-seeding-tips.htm