Your best bet with a lawn is to go with sod rather than seed as most of the good turf choices for your area are not available from seed. Weeds should be removed first. You have several options including rototilling the area lightly to destroy surface weeds and then laying the sod, or spraying with a general purpose weed killer containing glyphosate waiting a week and then rototilling.
For lots more great info on how to establish and care for a lawn in your area contact your local County Extension Office. They have free info on hand to assist you. The following web sites are also very helpful:
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