You can use one of the selective broadleaf herbicides used to control most of the common weeds found in a home lawn. A selective herbicide will kill the weeds but at the same time not injure the desirable turfgrass. Refer to individual product labels for specific recommendations. If thatch is a problem it should be removed now. Lawns that were made up of grass types other than Kentucky bluegrass may not require this step.
Power rakes or de-thatching machines can be rented to eliminate thatch layers.
It is necessary to rake off the debris resulting from the de-thatching process. It is very important to make sure that the seed you are going to apply is in direct contact with soil. Good seed to soil contact will insure optimum germination. Suppress the growth of the existing lawn grasses. Scalping the lawn by mowing it very short will do this.