Decide which type of mounting you want to learn. There are two ways to mount a fish: foam mounting and skin mounting. In foam mounting, a taxidermist skins a fish and then glues the fish skin over a foam replica of the fish's body. In skin mounting, the fish's actual body is preserved with a hardener and filler. No replica is required.
Read and learn everything you can about the type of fish you would like to mount and the type of mounting you want to do. Books can give you good information on taxidermy, plus some basic instruction, when hands-on learning is not an option. Consider "The Breakthrough Fish Taxidermy Manual" or "The Tom Sexton Fish Finishing System" to learn fish taxidermy techniques from start to finish.
Care for your taxidermy subjects properly before mounting them. This will ensure your finished product is of the highest quality possible. It also will prevent you from mistaking prior damage to the fish as your own faulty workmanship. Proper care for the fish you intend to mount includes not allowing the fish to flop around and injure itself and freezing it as soon as possible .
Buy instructional DVDs. A DVD can help you learn the art of fish mounting from a professional in the comfort of your own home. Choose a DVD specific to the type of fish you plan to work with. The American Institute of Taxidermy offers instructional DVDs by mail, such as "Largemouth Bass Mounting for Beginners" and "Perch Mounting for Beginners."
Attend a workshop. Workshops vary, but most focus on particular aspects of the taxidermy process. A workshop can help you improve your skill level in areas you may be having trouble with. Even if no taxidermists in your area conduct workshops, they may be able to help you find a fish taxidermy workshop elsewhere.
Take photographs of live fish and consider keeping the species of fish you plan to mount in a tank at home. This will help you study how the fish moves and examine its coloring.
Practice. The more fish you mount, the more adept you will become at fish taxidermy.