This is a general guide to the basic steps you'll need in order to create a comic or graphic novel from scratch. I've given suggestions for both hand drawn and digitally made comics.
An outline of your story is an optional place to start. Some people will want to dive right into the script or storyboards, but having an outline will keep you on track for plot and pacing. You will want to know before you start who your characters are and what motivates them. How will they grow and change as the series progresses and what will they learn? You may also want to make notes on your setting, especially if you are building your own world for the story take place in. Lastly, think about what the central plot and themes are going to be. Are you going to follow a three act structure? If yes, then what are all the story beats going to be and where will you have them occur in the story? Does your comic have a theme? A theme is an overarching idea that permeates the story. It could be something like "friendship" or "unity." It's something that your characters and their struggles will reflect.
An outline doesn't have to be a novel. It can be point form or a flow chart, but you'll want in idea of where your story begins and ends and the major points you want to hit in between. The longer your story, the more you may want to flesh things out before starting.
With an idea for characters and setting in place, you'll want to try drawing them before starting. It may take several iterations before you settle on the final style for each character and place, but that't OK because this is time to experiment with ideas! When you've found a design you like, you may want to draw character sheets as well, that show what each character looks like from all sides: front, back, side and 3/4 views. This will be handy to refer to as you go along and help with consistency.
Now we get down to the nitty gritty. Your script records the scenes and what your characters say, along with any captions the story might need. You'll have to decide the level of detail you want to express to an artist (or yourself if you are drawing your comic). Some people write very minimal scene descriptions and others are very detailed. I think it best only to mention things that are important or that need be illustrated in the scenes. For example if it's important that someone takes a bite of a hotdog in a panel, you will need to write that out. But if the characters are eating over a few pages, it might be enough to say that two characters and eating hot dogs on a park bench and leave the rest to be filled in as you go.
Above is an example of my script from my comic "Wolfsbane." You'll notice pretty minimal descriptions, because I'm the one drawing it, and so I'm going to make up most of that in the next section.
Working from the script, next we decide how the panels will be laid out on the page. As with the script, storyboards can be very rough or more detailed. You can use stick figures if that gets your point across, but usually a little more detail will help you when you get to the drawing stage. The point here is to make sure that things fit appropriately on each page. You might have one panel too many or need to stretch things out depending on your pacing. You can start with where you think the biggest or most important scenes should go and work around them, or just work chronologically. But if I know I want a double page spread near the beginning of the comic, I will have to storyboard that out accordingly.
Make sure your pages are proportioned in the dimensions you'll be using when you finish the comic. Also make sure you have some room outside the edges of the page for a bleed. (This is more important if you decide to print your comic, but better safe than sorry.) If you are drawing by hand and want to help yourself in future steps, then making your storyboards the size of the paper you plan on drawing on could save you time as you could just trace the layout onto a new piece of paper, or you can do this set up in the drawing stage and just use the storyboard as a reference.
You can do storyboards by hand or digitally. At any point in this process you can go from hand drawn to digital just by scanning your work and saving it as a digital file. You can then add layers on top of the original and continue the process digitally. (Make sure to create high quality files of at least 300 dpi to work from when working digitally, especially if you plan to print your comic.)
There is one intermediate step here I wanted to mention, if you think you need it (I certainly do), and that's to find or create reference photos before starting to draw. If my characters are in complicated poses, or there's something I don't know how to draw, like a wheelbarrow, I will go out and take photos of those things, so that I won't get stuck later when I'm drawing.
If you haven't already, set up the appropriate panels for the page, then roughly put in where your characters should go. You can refine your sketch as you draw. After the drawing is done, I will make notes if I think something needs to move or even be resized in a panel. This is easier to do digitally, but can also be done if you are drawing by hand, but will require you to re-draw a page or make a note to move the panel around when you are inking. I then move the sketch around, underneath the final inked page as I go. I'm still doing my drawings by hand,because I feel more confident with a pencil.
I've done inking in a variety of ways, either transferring the sketches onto a new piece of paper or tracing over them, either with a new piece of paper or digitally. Digital inking has its conveniences, but I'm still a beginner at this myself. If I'm inking by hand, I will trace or transfer a sketch onto a new sheet of paper and draw in the inks as I go. The process is similar digitally, though I have to say that moving characters around or resizing them to fit a panel better is a lot easier.
There are many methods to colouring a comic. I've tried screen tones, watercolour, and digital painting. You will have to decide what method is right for your comic. This is probably the most painstaking and time consuming stage of the whole process. But you've done a lot of work to get to this point, so take your time and be patient. If you are working in black and white, decide on a value scale that you can use throughout. If you're working in colour, decide on some palettes for your characters and scenes to refer to. I tend to focus on filling in larger areas first and then adding shading, highlights and other details after.
A common way to do this, when working digitally, is to work with "flats." This is where you block out a scene with big blocks of your basic colours in one layer, then add details in another layer on top of that. If you make a separate layer for the flats, then it's easy to select specific areas to work on, and if you work within the selection, you won't colour over another section.
Depending on where you want to share your work, you will need to prepare the pages for whatever media you've chosen. If you want to print your comic, talk to your printer about what specifications they will need. You will need high quality images of your work for print, of at least 300dpi for your pages. If you want to put your comic on the internet, then creating some jpgs will suffice. These only need to be as high as the highest screen resolution (100dpi will probably do, but things change fast in the digital world so check before saving). You may want to add a watermark with your name on it however, as things tend to get lost in the bowels of the internet. But if your name is on it, then hopefully people will always be able to find you and where you posted the original. Congratulations on creating and sharing your comic!