Access a good database. For general spider inquiries, mark down the size, color and other distinguishing features of the spider in question. Visit a site such as Bugfinder and enter the details you encountered along with the state of Florida. You will be presented with a list of photographs and names to compare with your findings. Florida, as of 2011, is home to at least 22 different species of spider.
Recognize the most dangerous. As of 2011, the state of Florida contains two types of spider that are extremely dangerous with different sub-species of each being present. The first are widow spiders and the second are recluse spiders.
Examine size. Widow spider females range between 8 and 15 millimeters long while males are considerably smaller at about 2 millimeters. Recluse spiders do not see such a disparity between the sizes of biological sexes. Each sex of this type are usually between 6 and 12 millimeters long.
Focus on the abdomen of widow spiders. Florida is home to black widows, perhaps the most instantly recognizable of all varieties. Along with the black body, this specie possesses a red marking on the underside of its abdomen. This shape is often compared to an hourglass. Each specie of widow spider in Florida has a similar red or orange marking in roughly the same place. Brown widows can vary highly in color. Red widows will have a black abdomen. The hourglass marking of a Northern Black Widow will appear as as a dissected hourglass or as a set of separated triangles. (see ref. 2)
Look at the recluse's eye pattern. The most common way for eye patterns to be observed on spiders is to see two rows of four totaling eight eyes altogether. This is not the case with the recluse. It has three pairs of two totaling six eyes. These spiders are often brown and their abdomens will usually not show diversity or give you clues as to their identification.
Watch out for the Chilean Recluse. This is the most dangerous of all recluse varieties. It is usually a sandier or yellowish color. Near its head portion, the Chilean usually presents a violin shaped mark but this is often less than helpful as many Floridian spiders share this characteristic as well as the size (around 15 centimeters). The violin mark is also quite difficult to see. The Chilean recluse, as of 2011, has only been found in Polk County, Fl., not near Tallahassee. Nonetheless, if you see any spider resembling this description maintain your distance and err on the side of caution.