I believe citrus harvest should be going on in Florida and that may be by far your best bet, Most of alabama and georgia just don't roll midwinter (too cold).
I've been working on pear and apple harvest this fall in Washington state and heres what i can say:
(if citrus there is anything like apple here)
1) knowing spanish is great. the workforce is 80-90% mexican and 10% other latinamerican. At least say hola and que paso and shit like that.
2) surprisingly almost all orchards are on-the-books, u have to fill out an I-9 and W-4 and get deductions taken out of your check
3) despite the prior, it is super easy to get a job. just show up, i got hired with a beer in hand at 8 am on one job, and on another my buddy and i rolled up on little kid's bicycles
4) if u have absolutely no experience, it may not be a bad idea to lie on your 1st picking job. by the end of the week you'll have it down anyway.
5) the "worksource" (like unemployment) office here has been great for referrals, i'm not sure what fla has
6) fuck the internet, it has nothing on picking jobs. just roll down the road and ask people. or if you see mexicans with pick-bags, ask them where they are working, find them at the bum feeds etc