I did one early this year... so far still weed free and it was terrible. here's what i did.
1. Sod strip entire area and remove
2. Till existing soil
3. Spread Triple Mix soil
4. Till soil to mix together
here the before afters. Gilmore Landscaping - Pictures/Work Thread
Good Luck, DO NOT guarantee it weed free.
My customer agreed to a fert program for the remainder of the year and I told her I would hand pull weeds for 30mins each fert application.