Plan ahead, plan ahead, PLAN AHEAD.
Do not go in thinking you can make up a long-running comic as you go along. If you want to maintain reader interest with tight storyarcs and strong character development, if you want to maintain momentum by always knowing where you're headed, and if you want to have scenes and storybeats to look forward to in order to stay excited about your series, it is vital that you plan ahead.
Every time I've failed at making a long-running comic, it's because I didn't plan ahead and painted myself into a corner or ran out of momentum because I had no destination to head towards, no story objective to make sure I was lining up plot points to get to, and no ultimate point or message to my series.
You should similarly plan things like your approach to making pages so that you know making them regularly fits around your schedule. Do test pages or panels ahead, test that your character designs aren't to annoying to draw a lot, and that the style you decided on, the way you're going to do backgrounds etc. isn't going to cause issues with making lots of pages.
Don't get distracted by side stuff
Oh boy, it sure is fun making Cast Q&As and fun seasonal or AU art, or pinups! ...STOP! Don't make ANY of those things until you've completed a chapter. Don't interrupt the flow of a chapter midway with fun silly side content like illustrations or the like. Firstly, your audience won't care until there's enough story content of the characters for them to want to ask questions or see them in alternate outfits or scenarios, but secondly, it will break your flow, and since illos and omake are easier than pages, can easily become a low-hanging fruit that tempts you away from the grind. Put extras only between chapters. You have to make your pages.