First thing to do is your research. The Department of Environmental Protection (DEP) has several publications that give you good guidelines. The 1996 Mangrove Trimming and Preservation Act, and a Mangrove trimming guide for homeowners are two good resources.

http://www.dep.state.fl.us/water/wetlands/docs/mangroves/mangrove_trimming_guidelines.pdf

http://www.dep.state.fl.us/water/wetlands/docs/mangroves/mtpa96.pdf