1. Fall is the best time to seed. You are probably too late to do this.My plan is to completely tear up all grass and weeds and prepare to re-seed next spring. My initial thought is to run over with disc to cut through and tear up the sod layer and then make multiple passes with something like a chain harrow to hopefully rake up as much grass/weed as possible.
2. Application of a non-selective herbicide such as glyphosate at this time of the year will kill the remaining grass and you'll be left with a topsoil erosion/migration problem for the winter and early spring. So leave what you have there.
3. Considering you want to reseed in the spring (again, not optimum for reasons I will explain shortly), apply glyphosate as soon as the weather turns. You will probably have to have a second go about two weeks later as well, as glyphosate is not a pre-emergent and you are going to have weeds coming in at the same time. I would not till, you will just bring more weed seeds into play. Instead, amend with a mixture of topsoil and peat.
4. Seed using a slit seeder, cover with light peatmoss, roll for good topsoil contact, cover with straw (not hay).
5. Water to keep seed/seedlings damp.
6. Fertilize after second cut.
7. Do not apply PRE-EMERGENT for about 3 months. This is the primary problem with seeding in the spring -- you can't apply a pre-emergent and the weeds are going to germinate alongside the turfgrass and compete. The fall is the easiest/best time of the year to get grass going -- far better than spring. You do not want nor have to worry about weed killer/crabgrass preventer when seeding in the fall, as these annuals will die off the moment the temperature drops below 50'F or so. Crabgrass preventer (aka "pre-emergent", tradename "Halts" or "Dimension") is applied in the spring, and lasts about 3 months. It prevents *any* seed germination, which is why you can not seed turfgrass in the presence of a previously applied pre-emergent.
In closing,
My advice is to wait until next fall. Seeding in the spring is haphazard at best. In many cases the roots will not get deep enough to fend off any type of summer drought, and then when the grass gets weak the weeds will multiply and crowd out the limp grass. And if you try to seed in the early summer you will end up with a splotchy lawn, and weeds will grow in the bare spots.
Finally, read sites such as
http://www.lawnsite.com/forumdisplay.php?f=100
Wrooster