Growing a quality lawn in south Florida requires more info than I can fit in a brief reply. Let me say that first you will definitely want to eliminate any perennial weeds with a weed killer such as one containing glyphosate (follow label instructions carefully). Then a soil test will help determine needed nutrients. Apply as per soil test and then rototill in a few inches deep. Then plant sod and water as needed to keep it moist until it has a month or so to get some roots down. Then you can back off on the frequency so as not to promote disease development in the turf.
For lots more info on starting a new lawn check out the following web site which is very informative:
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