Clean, Shape and Firm

[Grassman]

Remove all debris to at least 6 inches such as large rocks and old thick roots. Some stones are exceptable providing they are not putruding the finished seedbed.
Use clean soil on any areas that require landscaping.
Get the area to be sown exactly how you want it to look visually and then make sure the ground is nicely consolidated by treading well in or by use of a quality heavy roller. especially on made up ground or infill. This is vital at this stage as it minimises subsidance and unnecessary undulation in your finished lawn.
The golden rule is roll, roll and roll again. If you can ride a pushbike over your seedbed without sinking into it then you are now ready to create the fine tilth prior to sowing.