New Lawn HELP!!!!

Hi Everyone

My back garden is a Lumpy, Hard, Uneven mess of a lawn. There are hard tufts of grass in places to thinning or bear patches. At about 10-15cm its a thick clay like material & the garden itself is 10mx7m in size.

I've had enough!! so i have a plan but being a complete noob to gardening i thought id lay my grand plan out and let everyone here tell me why thats the wrong way to do it....

* Hire a rotivator and thouroughly rotivate the garden until i am left with as fine a soil as i can get.

* Rake the soil until i'm left with as even a surface as i can get

* Plant grass seed using a seeder

* Re-Rake and Roll the garden

What am i missing, forgetting, unaware off or doing wrong? I'd like to hire the rotivator for next weekend so i want to prepare and research as best i can.

Any advice would be appriciated.

Cheer
Alan