As UpgradeMe said, It would really help if you would tell us which airline(s) you plan to fly.

21 days advance is almost always best for fares. You might consider departing FLL rather than MIA as it is a WN (Southwest city, it is also a Spirit and ATA city). Try nesting. Try end to end.

Please pause 5 minutes before posting responses that cause some of us not to respond. Clarity and good sense helps immensely.

Cheers.