By far my least favorite thing to see when I start a story (particularly fantasy genre, or other non-Earth settings) is the dreaded info dump. No one needs several pages or especially a whole chapter/prologue doing nothing but explaining the world, its systems, and its history to us up front. It's the most boring way to present that information, and does nothing to help us, the reader, before we actually know about any of the characters or story. Like if you need a couple of pages to set up the immediate premise, awesome! But no history lessons (or other types of lesson LOL) please!
I agree with @arisu_kosuta ! A typically safe way to start a story is within some interesting scene, or "right at the action". We get a crash course with the characters, get a taste of their personality and circumstances based on what's going on in the scene, and if you choose an effective scene it can be a good way to hook a reader!
Another thing I think is important when planning the beginning of a webcomic is like... think about how fast you can draw/how fast you're planning on putting pages out, and plan accordingly. Ideally the super early introductiony stuff shouldn't last for months and months worth of updates (unless it's particularly interesting) because that kind of stuff is a slog for readers to get through. My go-to example is like serialized weekly manga. They put out a full chapter a week, so stories like that can potentially afford to have a chapter or two of "slow start up" because they blaze through it. The average hobbyist webcomic artist puts out like 1-5 pages per week is all (usually close to 1-3). If you took 2 chapters doing introductions, it might take a year before you get to the good stuff xD Webcomics are by nature kind of a slow medium, so it can be useful to start at the good stuff, so your readers can engage right away.
(although of course that's not the only good way to start a comic. There are endless possibilities. But starting in the action is a safe bet, usually).
