I didnt. It all just came to me like a direct download from somewhere else...
@kyupol haha maybe I should update myself and download it aswell 
I started writing it as a straight up novel actually. Got through to about Chapter 5 of my comic in terms of plot, with the rest of the story loosely planned, before starting to work it into a comic.
@DexterityMaxity I'd probably say I'm operating below 50%- but it's a strong "below 50%". Like now- I'm kinda struggling to finish off scripting Ch 2(which I will be starting on soon), but I have a clear idea of what's going down in Ch 3. I have a gist of the main story going on in Ch 4; I most likely will be introducing another element as well coz the main part of Ch 4 is generally the prominent plotline of the whole series. I have an idea of where I'm going with the series for the most part, but it's the "filling in the gaps" that is challenging.
I think as long as you have an idea of that larger plot in mind it will help in "seeding" up to it. Like you can add hints to something greater in the early/middle episodes. Then your readers will think you all the cleverer, haha.
I agree! I think it's very important to have an idea how you want it to end, even if it's summed up in a single sentence. The stuff in the middle can easily be changed, as long as it leads up to the end you want.
SAME XD
In my current story, I'm actually in the middle of changing how the scene goes! It's fun and frustrating all at the same time.
Like a lot of people on here Shadowbinders7 has the ending and major plot points planned first and the rest is made up as we go along.
My comic had its beginning well planned out as basically it wasn't originally to be straight up a gag-a-day, but shortly after when I knew I wanted to introduce more characters as time went on, I had to start creating backgrounds for many of my characters.
Over time, I devised all the character pasts and where I planned to take them in the future, and if I were to decide to end my comic, have an ending in mind. But it hopefully won't be still for quite some time before that happens.
DON'T READ THIS !!!!
I'm so impatient that i uploaded my comic when i had an idea of it and that was like living it my self , but problems were starting pop out like hell , so don't do that 
, i almost killed my protagonist xd , My advice is to write your story down first , then be open for some changes in the process . I hope i could follow all this advices from expirienced comic makers but i can't ahahah , I love to improvise...thats how i am...having fun , that's the most important, enjoy , creation is the most beautiful thing in the world , woahhahaha i'm crazy !!!!!!
Having an idea how you want your comic to end is a good idea so that you're always working your storyline to eventually reach that end. For me, I've been working on my comic for many many years and I know how I'll be ending it, down to the last couple of chapters and even the last scene I plan on using. I also have a good sense of how I'd like the story to progress, but sometimes I end up revising or reworking entire chapters because I need certain characters to grow or develop in different ways while still keeping in mind where I'm ultimately heading.
I guess I'd say if you can think through where you want your story to end, that would be really beneficial to you in the long run.
I actually spent about a year rough-draft-storyboarding every page of my comic before I let myself start drawing any final pages. But this is because I'm the sort of person who gets stressed out by uncertainty very easily; I knew that if I started trying to keep to a weekly schedule without having an exact path, I'd get discouraged the moment I ran into a plot point I wasn't sure how to address, or start going off on a tangent, decide I hated it, and stop drawing the comic entirely.
Forcing myself to outline every scene and dialogue before I started gave me some freedom - I could put a draft down for a couple days and come back to it when inspiration hit, without having to worry about the next update being due soon. My case is probably an extreme version though, and I have a relatively short comic I was actually able to plot from start to end. Everyone's situation varies.
I had a start, I had an ending and I wrote a basic outline of the middle.
Then, I broke the story into one line summarized scènes. And now, I script the scènes separatly. It give me some freedom but stop me from getting carried away and writing unecessaries scènes, drifting to nonsense and full of plot holes, like I tend to do when I don't plan a story.
@DexterityMaxity Well, I've drawn ~160 pages for Remember1 so far and the plot is only now approximately planned out =) I'd say I have the most important scenes planned out, which would be ~40%, the rest will come with drawing on.
The "Problem" is: From the main plot I had more than 40%, but since I want to tell some of the side characters' background stories it kinda adds up to the plot! 
Very precise, but also very loose at the same time. It was and is basicly a detailed outline that describes the most important parts of the story. For some strange reason the first thing I had in my story was the last sequence of the ending. It was inside my head for almost 5 years before I even knew I would start seriously making comics at all.
It is always kept very loose. That way I'm able to easily change, take out and put in things without too much hassle. And it makes the whole thing more spontaneous and lively.
But some projects I just start without knowing where it will end at all. One of my all time favorite comics "The Airtight garage" by Moebius was pretty much improvised. He made a short chapter of 2-4 pages every month. And he never really planned what to do from one chapter to the other. And as the last chapter of around 15 pages he tied everything together. It is a highly interesting book.
Akira Toriyama who drew Dragon Ball also once said that he didn't really plan ahead too much.
I have planned all the basic steps/points into the end, but the journey to point B from point A may subject to change.
I remember finding that work by Moebius fascinating in its own way, in large part because of that very quality. I also had heard that from Toriyama-sensei, who has always been very honest about his motives in doing comics; in one interview, he was engaged about his sweeping natural landscapes and his tendency to set the fights in such places in nature, removed from the urban sprawl. He replied that he just hated drawing cities and buildings, so he avoided it whenever possible!
Personally, regarding the original question here, I never have an ending concretely planned for a series. Things change, circumstances change, you'll get to know the characters and circumstances, and to be quite honest, unless it's a very short story and you're writing it for a very specific point, you probably won't be well-served by too rigid a concept of the ending. Of course, you can have a general idea of how you'd like it to end without being too intractably written in stone, and that's what most people who plan that far will do, as @thomasfallaeriksen pointed out with his own approach.
When I plan out individual stories and chapters, of course, I tend to have somewhere I want them to end up, but I'm not afraid to change that depending on how it goes during the chapter, in little or large ways. Sometimes the planned ending doesn't work out at all, and it has to be changed significantly. But I'd rather go with what feels right than to stick with my original idea and feel uncomfortable with how it turns out. So many things change, inevitably and invariably, during the process of writing and creating. Sometimes even the visual impact alone sways how a story will go.
I usually have some idea of a desired resolution, several points along the way I want to illustrate, and then I work with those things in development. But I wouldn't want to leash myself to what I think is a good idea before I really get to know the story, the circumstances, the characters, and quite importantly -- especially in indefinitely ongoing series -- the readers. A writer's approach is very important here, and it can make the difference between readers feeling appreciated (which does not equate to pandering, n.b.) and readers feeling resented, or like the writing exists to spite them. Sometimes being utterly disconnected from readers, for the sake of sticking to a plot developed long earlier, can be a harmful thing.
So there are many considerations. "The best laid plans" and so forth! It's just not a simple question with a simple answer. Even if you plan out in detail, you're inevitably going to have to change something, sooner or later, so I think it's best to try and be flexible in most cases.
My comic started autobiographical so it was just gonna be going until I got bored but then it really got off the rails and is a complete bonkers nightmare town where you can just catch a meteor in a box and blast it back into the sky I guess. I've since been trying to solidify the ending but I'm more or less making it up loosely based on actual events. It's mostly one page goofs but sometimes there's story arcs and working on those pre-planned bits gives me enough time to think up more stuff for the next part.
I'd say I've planned it pretty well. I used to do scripting in the first chapter, but I sort of gave up on that since I come up with the best(=dumbest) jokes while I'm drawing the page, so having a scripted dialogue kind of became pointless, as I hardly ever followed it, but when I did the flow of the comic was disrupted. Like if I'm reading chapter 1 & 2, I can tell that the jokes/silly scenes in ch 1 are very try hard sometimes, and those are the ones that were scripted beforehand. The flow is much more natural since I gave that up after ch 1.
But I do still have a written outline for what happens and when it's supposed to happen. Sometimes I change up the setting or add a scene here or there, but mostly I follow the outline that I have, since foreboding is easier to sneak into previous chapters if you have a clear image of future conflicts & events, which prevents some events in the comic feeling like they just came out of the blue ( I mean, my hints are very few and far inbetween, so sometimes readers still feel like that, but hey, I tried :D).
So to quit rambling I'd say having a plot synopsis goes pretty far, but it's completely up to how you work if a detailed script would be helpful or not.