Fresh or frozen, banana leaves are not only wonderful functional plates in Indian and Malay cultures, they are also used for wrapping fish with chili sambal and grilling. Most of us will buy them frozen.
Defrost them at room temperature.
Wipe with a damp cloth or paper towels to remove any white dust they may have.
Passing them over an open flame not only makes them pliable but brings out their naturally deep green color. (You can also quick-rinse under hot water, and then rinse under cool water to make them much more pliable).