There's an easy way to understand which states in the US are Democratic and which are Republican. Roughly, along both coasts, the states are Democratic, while the more inland one travels, the more Republican the states become.
Florida is an exception. It is not just a swing state (which means that its verdict doesn't follow set pattern), it swings with a huge number of electoral college (29).
In the US, the president is elected not by the popular votes but the number of electoral college votes from each state. The candidate who gets 270 or more wins. Even if the victory is by a wafer thin margin, as per the winner takes all tradition, all the electoral college votes of the state go to the winning party. The other swing states, in comparison have fewer electoral colleges—Nevada (6) Arizona (6) Utah (11) Idaho (6) Wyoming (10) Ohio (18) North Carolina (15) New Hampshire 4 and Georgia (16).
While Trump is ahead in swing states like Ohio, Hillary seems to be having the advantage in the desert states.
Florida's cruciality also comes through because of the way elections have panned out in the last few hustings. In 2000, the margin between Al Gore and George Bush was so slim that he actually sought a recount in the Democratic leaning pockets of the state. The court struck down the recount as unconstitutional as per rules existing then, and Gore had to concede defeat.
In 2012, Florida was the only state decided by less than 1 per cent, with Barack Obama getting 50.0 per cent of the popular votes to Mitt Romney's 49.1. Florida turned swing due to its recent demographic changes. It was Democratic like most southern states to begin with, then it turned Republican in 1952. Over the last half century though, Florida has followed a different growth trajectory than its neighbours. Its resorts and theme parks have attracted numerous migrant workers, while it's seen as a haven for retirees, too. NASA's launch site in in Florida, as are resort towns like Tampa.
Various projections show Hillary to be having an edge in Florida, some surveys give her a three fourth lead. Winning Florida therefore is crucial, and not surprisingly, both candidates have put their energies into wooing it. At least seven rallies have been planned across the state between October 24 and November, with Hillary, daughter Chelsea and vice presidential running partner Tim Kaine slated to speak at various events across Orlando, Miami and Tampa. Trump too, has focused his energies on Florida even as he nurses Ohio, where he hopes to get the bumper 18 in his kitty. For Florida, his camp has at least five events between Monday and Tuesday.
Florida is called the Sunshine state—the warmest and southernmost of America's mainland states. The sun will also shine on whichever candidates wins Florida.