-A run down of why most comics end up dead after just a few pages.
Hyping It Up Before It Exists
A lot of people will put up promotional artwork, covers, character references, and other related work for their comic before putting up a single page. People often say if you want to write a book or you want to lose weight, it's best that you not tell anyone. When you tell someone you plan on doing something, they will praise you for it. The problem is, you are now receiving praise for something you haven't actually done yet. You don't have to work for that praise; the mere act of saying you will do something rewards you the same external way you would get for actually doing it. Sadly the result is many people are content to stop there. It's not even a conscious decision, but a lot of people will get caught up in the hype without realizing how hard making a comic actually is. Hold off putting up anything related to your comic until you at least have a few pages up; it will be worth the wait.
Spoiling Their Own Plots
Alternatively, don't put up any work that explains your comic, the characters, or their backstories. The reason for this is a comic should stand alone, without additional material explaining things to us. However, many people will give away important details about their story before it even comes up in the comic. Don't tell us your character's history on their ref sheet, reveal it to us over time so that it impacts the story. Don't tell us that someone will become the bad guy eventually, let us find out by their actions. If you haven't shown the event in the story itself, you shouldn't put it anywhere else. Don't spoil your own story.
Working Without A Plan
Don't make up your comic as you go. Too many people start with a vague idea, and go only so far as planning out each page as it comes up. This is why so many comics waste pages upon pages with nothing happening. I've seen comics where several pages are spent showing a character getting up and walking over to something, with nothing else happening. An entire page wasted. Each page takes countless hours to make, and when a weekly update is a far-fetched idea for most casual comic makers, that means it may be another 2-3 weeks before you see another page. Don't waste your pages. Plan out your story several pages in advance, so you know where it's going. Don't waste panels on pointless dialog or pointless scenes. On a related noted...
Not Managing Time and Effort Properly
Stop wasting your time and effort on unnecessary details or scenes. You need to find at what pace you can work that is best for your quality, and well as quantity. It's a common saying that artists want to focus on quality over quantity, but when you're telling a story the better story is the one that is finished. Not the one that stops at the beginning, or two chapters in. You won't be able to make every page as high of quality as your regular artwork; that's just not realistic. Simplify your art. I'm not saying for you to scribble and slap on colors, but find the balance that works for you, and your story. If it takes you one month to make one page, that is 12 pages a year. Where is your story going at 12 pages a year? Refer back to your script often, and keep in mind how long each page takes, and how long it will take your story to reach each plot point. Plan and draw accordingly.
Pick a schedule that is realistic for you to work at, and update your comic according to that schedule. When a person says they will work on it 'whenever', that tends me mean 'rarely ever'. Set deadlines for yourself, and make a habit of keeping them. It's very easy to put something off when you have no due date.
Wanting To Change Things
Even when a comic does get past its first 10 pages, too many creators want to go back and make changes. Either to the art or the story or the characters or what have you. But this often starts a loop of constantly editing without progress. Fixing things like typos and off-model errors is one thing. But don't go back to change your story. Yes, the longer it takes to tell your story, the more it will evolve on its own. Instead, force yourself to build upon whatever already exists. Imagine that you have laid down the foundation for a building. You can't change that foundation, only build upon what is already there. The best stories are those that have placed some limitations on themselves, and you will find that if you are creative enough, you can work around whatever elements you disliked to use them in your favor. As for art, most comics have bad art at first. But your time is better spent progressing the story, not retreading old waters.
Starting From The Beginning (IE: Birth)
We don't doubt your character was born from another living being. You don't need to start from their birth to prove us this. Unless your character is a child for most of the story, there's no reason we need start with their childhood. Events that happen in their childhood can be brought up later, but start the story where the story begins. Not where your character began.
Creation Myths, Dreams, and Ancient History
Similarly, we don't need a story on how the universe began. If your made up religion is seriously important to the plot, then show it being important to the actual plot (meaning the conflict of your protagonist). Bring it up when it becomes relevant, but don't give us a history course from page one. Besides being a tired old cliche, it takes too long for the actual story to start. We are not here to learn about the world's religion, we're here to see the characters and their journey. The longer you take to start that story, the less invested we will be. This is also why you don't start on the ancient history about some ancient war. It's less time for the reader to get invested in our protagonist and their conflict. Focus on their story, not the one that happened years ago. And never start on a dream sequence, because it's wasting space and does not progress anything. It's wasting time on events that didn't happen, and misleading the reader unnecessarily.
A bland protagonist will bore both you and your audience. Remember there's more to a character than a few tacked on traits and a backstory. A good protagonist has flaws (not just physical ones) and will develop over time. Their decisions and mistakes fuel the story. A character who is always right and always makes the right choices is not relatable.
Not Earning Our Sympathy
You will not have our sympathy, investment, nor attachment from page one. You will probably not have it for at least 15-20 pages. What this means is that whatever horrible tragedy you show us before then will have very little impact. If anything, it will come off a bit silly and forced. If you start your story by showing us the evil overload slaughtering children, or our protagonist mourning the loss of their parents, it's not going to have any affect on us (the audience). We don't know these characters yet. We don't have any reason to feel sorry for them. You have to build that relationship between the characters and the audience. So save the tragedy for later, when it will actually meaning something to us.
Starting For All The Wrong Reasons
Creators most commonly quit their comics because they become bored. That's also because they started their comic for the wrong reasons. A writer makes a story because they have a story they want to tell, that needs to be told. It's not because they want to show everyone how awesome their story is, or to impress everyone with how cool a character is, or to come off looking dark and edgy. They have a story that they love so much, have poured so much of their soul into, they simply have to tell it. They are driven to tell it. Artists don't realize how mind-bogglingly time consuming it is to make a comic, especially as a hobby. It is a labour of love, and if you don't love your story, there is no way you're going to get anywhere.
Not Having Fun
Too many comics start off way too seriously and take themselves way too seriously. Yes there is a time for drama, and being dark and edgy. But you have to earn that first. You have to enjoy what you're doing and have fun with it, which means not making all of your characters brooding tormented souls. So many of the best stories have found their balance by starting light-hearted. Once they have earned their audience's attention and investment, they start to become more dark and serious. But you have to earn that first. Both from your audience, and yourself. You have to be entertained by your own characters, and your own story.