I think it's interesting when people ask this question. it's not a bad question to ask it shows that you are willing to do what it takes to dive in but honestly, there is no Right or wrong and there is no particular order in where to start because it all depends on how you want to tell that story.
with my own comic. it started with an idea. my idea was to write a story about a obese guy who never found love growing up untill he met his partner. that was ALL i had and i dived right into it.
not saying you should do it this way, but it is important to "TAKE A DIVE", if you keep pondering, "where do i start", "how do i go about this", "is this the right way" you will "NEVER", get anything accomplished and you will never start.
when you make the decision to start, and you actually start creating scenes and panels and drawing your characters, you will learn what works for you in the process.
so my dear, START. dosen't matter if you start in the beginning or end or tell it backwards. just start and then, you will know what you want and how you want it.
sorry for long message. i hope this helps.