For reference, I lived in South Florida through my early childhood and continue to reside there now. I think Floridians are pretty immune to having a regional accent unless they are ESOL people. At least, if someone asked me to define a (South) Floridian accent, I'd just say that it's the same thing as General American.
I remember than in Elementary school, I would pronounce voiced 'th' as 'd', though I think that voiceless 'th' remained 'th'. I noticed this one day and subsequently tried to "fix" it; I now pronounce it "properly".
I also slurred my speech a lot. I'd say "yer" instead of "your". I'd even add vowels: "I do declaruh" (the adding a schwa after voiced consonants thing is pretty common where I live, but "declaruh" sounds distinctly southern) and "go to the fairuh". I don't do this anymore.
I have a feeling that I also dropped some 'r's, which is why in Middle School many people took to asking me if I was British (coincidentally, Middle School is when I first made an attempt to start speaking more clearly).
Something rather interesting is that I don't pronounce the 'r's when singing; "pearl" becomes "pea-uhl". My accent becomes non-rhotic, I guess because 'r' is a rather ugly sound and I don't like pronouncing it. :x