Creators can sell comics as the usual 24 pages or as a graphic novel 60 to 200 extra pages. When one wants to sell comics as a 24-page book, the comic would have to come as a series of separate issues. In this way, it may be cheaper to produce. You can have a series with 5 issues that come out in different periods of the year. The revenue made from issue #1 can be used to cover the expenses for issue #2. In my opinion, this is probably the best way for inexperienced comic book creators to start.
However, if a creator thinks that making a graphic novel is more convenient for him/her to start with, you can go for it under two conditions.
You have the funds and a marketing plan. I say this because the marketing is the most challenging part any creator experiences when producing a product. These days publishing your comic book doesn't have to take fifty dollars out of your pocket if you do the writing and drawing yourself. This method is known as printing on demand. For first-time comic book creators, the difficulty of marketing your comic book can be ten times multiplied.
Authors who successfully sell comics they created are usually those who have experience and background in the producing of comics. It would be easy for someone who is known for working on titles like X-men or Spiderman to come out of Marvel and produce his own comic books and sell it. This was the case for Todd McFarlane. McFarlane reached star status in Marvel comics. When he came out of Marvel, he was involved with other illustrators in starting Image comics. Once he published his title called Spawn, it became an almost instant hit because of McFarlane's popularity.
The thing is, not everyone who wants to create comics would get the privilege to work for a giant publisher like Marvel Comics, and also not everyone who works for Marvel will become popular.
There are two ways one can break into the comic book industry by creating comics and selling them. Both methods involve developing a name for yourself. First, it could be done by integrating oneself with existing publishers and editors, getting hired as staff in an editorial office, and getting published by a smaller publisher. The second way is by independent publishing. Let me add, both methods are complicated, and can take years to get positive results that could cost you big time money.
The encouraging news, there are other methods to get your work to audiences for less money or time. Thanks to the increase in technology, the conventional (going through the big time publishers) way of breaking into the comic book industry to sell comics are not the only way. I'll explain.
The hardest and biggest hurdle comic book creators have to overcome is marketing their comic book or getting an audience to their comics. Once people know that your comic book exists and like it, selling your comics would be a lot easier for you.
First of all and most important is that when you want to sell comics, you have to have a good quality and appealing comic book to sell. Develop an attractive comic book that you know a particular group of people would like.
The next step to sell comics is to market it to those people you made the comic book for. The people whose needs your comic book is meeting. In this way, you are almost guaranteed to have a value. You can do this by creating a website for your comic book and then refer interested people to the site to check your comic book out.
Creating a comic book and marketing it through the internet is now one of the most convenient ways to get your comic book recognised. Like I said before, once your comic book is known and liked, to sell comics would be natural.