One of the most important things to remember when stretching is to warm up prior to a stretch. Muscle is similar to silly putty in the sense that it is less pliable when cold. A cold stretch can sometimes do more harm than good. However way you train for surfing the one thing to remember is have fun . Because if its not fun, chances are you're not going to do it.
Surfers are inherently fun junkies, so keep the stoke and have a smile.