I've been telling my own stories through my comics now for over 20 years. For a couple of those years, one could argue that I possibly even did so WELL. As such, I've had time to put together a few specific thoughts on the approaches I often take to telling a story in the serialized format of comic books. I've found that It tends to come down, for me, to 3 basic approaches that I use one or all of at any given time.
The first, and probably most professional and "correct" approach involves making a defined, structured roadmap before the pencil ever touches a sheet of bristol board. This means forming your concept, characters, plot, issue-by-issue breakdown and page-by-page script before starting to draw. This is probably the most efficient and technically proper way to do ANYTHING, really. Of course, it's the approach I use the LEAST.
The second way to do it is the LEAST professional or "correct" approach and is best described as "making crap up as you go along". Also known as pulling it out of your posterior.
The third approach is a blend of the two thoughts. Plotting out your overall series (in the event of a finite story) or arc/s (in the case of an ongoing comic with running plot lines) in advance. Figuring out the basic beginning, middle and ending before you begin, while leaving the exact journey loosely defined and open to interpretation during the creation of each issue. THIS is what I prefer to do more often then not.
It's certainly how I'm approaching my current comic, "The Wellkeeper", and is an approach I discovered I liked the best while working on my online comic strip, "Dandy & Company".
About 10 plus years ago, give or take, I was working on a science fiction comic called "SCARRED WORLD: The Chronicle of Aegis". It was a full color, planned 6 issue adventure epic. To date, the first 4 issues were completed before the series was essentially put on indefinite hold while I shifted my focus to the "Dandy & Co."strip. Part of the reason that I ran out of steam on the project had to do with my decision to develop it with that first approach. The entire series was written out, roughed out and designed in advance of starting the first issue. I worked out all the details and had everything figured out before the proverbial first "shot". It was very efficient and very BORING.
I knew everything. I knew what was on the next page to be drawn and the ten after that until the final page of the series. I wrote it out, sketched it out and roughed it out. In my mind, it was done. And in the end, that had a big part to do with my loosing interest in the title. (I'm planning on re-printing the existing 4 issues to see if there's enough fan interest in rebooting the series this summer, but that's neither here nor there.)
On "Dandy & Co.", I had a set premise and defined characters, but no overreaching plot at first. It was a comic strip designed initially to simply stretch out forever. By design, making it up as you go along is almost a requirement unless you want to make a cookie cutter, formula strip. After a while, the bug for extended story lines bit me hard and the strip began telling multi-MONTH plots that ran day to day. I would always have the general idea laid out, but never anything more then a few strips written in advance and a general idea of where I wanted things to go. But because I was telling an ongoing strip, I could throw out my planned ending for a fun NEW idea literally at the last minute when inspiration struck. And, fyi, I often did just that. It was a lot of FUN working this way, but wouldn't work for something that is designed with a definitive ending.
That's where the balance that I'm using to work on "The Wellkeeper" has come in. I have the whole series very roughly plotted. I knew the beginning, middle and BASIC ending before I started. But the individual elements that happen issue-by-issue are left up to me to discover along the way as I'm working on each issue. As such, character relationships can grow and evolve in ways I wasn't planning on. Events that might have been planned for one issue might be moved to another because a more natural story flow was discovered. Basic characterization might change once I'm knee deep in the characters LIVES. It's much more chaotic and much less "professional", I suppose. But it's also one of the perks of self-publishing. I get to do things my own way and keep making comics FUN.