I'm also working on a webcomic; I've been chipping away at it over the last year and I still have so much to do! I've been in the same position as you, so hopefully I can shed some insight; let me know if you have more questions!
A good thing to nail down ASAP is the scope of the project. Know your upper limit on how big you want it to be, and be aware that these things always take years longer than you expect. Make sure you are setting yourself up for success by knowing what you want it to be. Is it serialised or episodic? How long is the story -- how long are individual arcs or acts? What plot beats do you want to hit and how long will they take to cover? If it is a long project, plan for your interests and availability to change over time.
For example, I know I want my project, Breaker, to be a long-term project. It is informed by sci-fi television like Star Trek and is about a crew of cadets finding their way home, so I want it to be episodic -- individual 'episodes' dealing with contained adventures and new worlds. This has the capacity to get unwieldy and over-long, so I have a plan for the winding down of the story leading to the ending so that it doesn't stop abruptly. I'm also keeping specifics open and have a premise that can handle changes in my interests to avoid losing motivation.
I don't know how familiar you are with creating webcomics, or how far you are in your development of your story and characters, so I'll tell you what my general development approach has been. Premise -> Main characters -> Immediately relevant worldbuilding -> Rest of the cast (it's set on a spaceship with a crew of ~50 so I can't make up random faces for the backgrounds
) -> Main character arcs -> Brainstorming other events/episodes/etc -> Working out which bits have to go where relative to each other and filling in the gaps -> Fill in the events of each issue/episode/chapter (where I am now) -> Finalise designs for cast and their environments -> Make the 'pilot' to test your practical workflow! This is script, thumbnailing, sketch, inks, (colour,) lettering. Lotta steps! So it's important to break it down in a way that works for you; not all of this will work for your project, but try to feel it out and make sure you're going in prepped without burning out before you start!
EDIT to say that with smaller-scope projects, you may not need as much prep work
I've been fiddling with some shorter comics that I've put much less development time in just to practice those muscles! I've got one open now that's just four pages and has only taken a few days! This is why nailing down scope is vital! Know what you want!
As I said earlier, if you have any specific problems you're bumping up against (I was struggling with episodic structure for aaaaages), just ask! There are lots of people here who can help!