Plan it out first.
When I started doing webcomics--and no, it wasn't Idle Tentacles or Mecha and Stem, it was WAY long ago--I didn't have a single clue what I was doing and I just went by a page by page basis. I would change what would happen in the story based on whether or not I could draw what I had been planning on drawing originally. There's even a page in one of my old comics where I couldn't draw a crowd of people so I just wrote "insert terrified crowd feeling THIS-a-way" and then drew an arrow pointing out the doorway.
At least if you plan it out, if there's something in the comic that you recognize you're not very good at drawing, you can practice before you get to that point.
Don't worry about vigorously keeping a schedule.
Honestly, people always get on this about how important it is, but if you have a couple instances where you miss an update, it's not the end of the world. I'd still say that it's best to have a specific day of the week when you upload the pages of the comic, and you should try to keep that as consistent as you can, but life happens and we can't always keep on top of that AND webcomics. As long as you get back into the swing of things once you're back on your feet, I don't think it's an issue.
I feel like this matters even less if it's a comic you plan on publishing. On one hand, it might help you keep up with working on the book consistently, but you also might get to the point where you're rushing pages. So don't feel pressured to rush the work to keep a weekly schedule. Just skip the week, finish the page and update it the next upload day. You might even get a little ahead of your own schedule in doing that. In that sense, publishing online is also just a means of letting people know the comic exists and showing them that it's something they might like to keep reading. I read a comic called Shadoweyes online, but two Shadoweyes books have already been published and the webcomic is WAY behind the published books. It's just a way of reading it for free and you really should be focusing on the published work because that's what helps keep the comic going.
Try to keep consistent in each chapter/issue.
It's good to try and keep each chapter or issue consistent in art style. Even if you're stretching the comic out for a long period of time and you've since progressed in your art, keep drawing the way you've been drawing until the chapter/issue you're on is complete. Then you can update the art in the next one.