Coral reefs are very diverse and have been coined the rainforests of the sea as there are many different species that live within a coral reef ecosystem.  There are similarly many facets of the coral reef to monitor, and your level of expertise will determine what level of monitoring you will be able to participate in.  So that the data is respectable it is important that your skills are sufficient for the undertaking of the methodology you will participate in.  For example, if you cannot identify reef fish by the species, it would not be practical for you to participate in reef fish surveys.  For each level a mandatory prerequisite is the ability to snorkel and record your observations.  What skills do you have and what level would you be able to participate in?