We embarked in Valencia, not the easiest of experiences as the local cab driver tried to take us directly to the ship rather than to the ferry terminal which is where we needed to check in, and when we did eventually find the terminal all was not clear. We were embarking as people were dis-embarking so there were a lot of people hanging around and no clear signage about where we needed to go. For your information the steps are as follows
1) Got to the luggage drop off on the ground floor, check your bags in
2) Go upstairs to check in