Yeah, there’s honestly a few easy ways to make FL blue (or at least keep it a competitive purple). #1 is to value and restore people’s voting rights in the state, and there was major headway on this with restoring voting rights to felons who have served their time. Last estimate I saw put this at around 60k votes for Democrats, net, enough to flip the race to Nelson and Gillum if they had been able to vote in 2018, it looks like. If Florida (and SCOTUS) had actually valued the votes of Floridians, we would have had President Gore in 2000, and possibly 2004, which would have meant FL voting Democrat for President would be the norm for the last 20 years, rather than the exception.
#2 is to actually take Florida seriously, which Nelson (and Clinton in 2016) kind of didn’t, as @
Skroe keeps saying. This is a larger problem with the Democratic Party as a whole, where they don’t take races as seriously as the should, but it looks like the house and Governors have at least learned this lesson. Hopefully Senators and the nominee for president in 2020 will too. Gillum I think did take his race seriously, but he’s also at a disadvantage because racism.
#3 is changing demographics, but Democrats shouldn’t rely on that. Demographics will change Florida, Texas, etc. blue slower than the party thinks, in my opinion.