Typically a shark will signal they are ready by taking a unique poster, slowing or stopping their movement and then opening their jaws. The cleaner fish will then take its cue and move in to begin inspecting for parasites in the shark's mouth and gill area.
The video was taken in the Maldives and was posted by Jr Waterworld. It is a 1:46 in length. We have also included a second video from 2008 showing a whitetip reef shark getting a cleaning service in Makena Landing, Maui, HI.