Throw down Scott's weed and feed (following instructions as to dampness of weeds, leaving it on them, no rain in next few days, etc.). That will kill most of the weeds. Wait about 3 days or so and throw down seed. Wait another couple of days and mow weed lawn down to as low as your lawnmower can handle. Continue seeding periodically and apply weed and feed again in about 6 weeks. Not perfect results, but fairly good (what I'm doing) and also fairly economical and fairly lazy.