Make sure the topsoil is good, at least 8 inchs deep and that there
are no significant rocks. HAve the PH tested and adjust with lime now
if needed. With new topsoil like this, it usually is required. If
the topsoil is not real good, then now is the time to fix it by adding
whatever is necessary, typically that is organic matter.

Then use Roundup to kill the weeds the last week in August. After the
weeds have died, mow them down short. You can reseed in 7 days, with
a rental slice seeder. Choose the appropriate grass depending on what
you like and what does well in your area. Buy it from a good seed
supplier, you can find these online.

After seeding, cover the area lightly with weed free straw or even
better a light dressing of peat moss. Keep it constantly wet for the
first 2 weeks, until germination occurs. This usually means a few
shallow waterings a day when it's not raining. After that, begin to
taper back the watering so it's less frequent, but deeper. At the end
of two months, you should probably be watering about once every 3-4
days, unless it has rained.