The cabin crew ranks goes something along the lines of:
Instructor
Chief Purser
Deputy Purser
Flight Attendant
You can tell the seniority based on the uniform. Uniforms for Chief Pursers have orange pinstripes, while Deputy Pursers and Flight Attendants have white pinstripes with either a gold band at the cuffs for Deputy Pursers, or just a button at the cuffs for Flight Attendants.
I haven't seen an Instructor before, so I'm not sure how you tell the difference between a Chief Purser and an Instructor.