Here are some tips that I have, not the great thing but anyway
Size: Work on a bigger size than Webtoon's (800 x any lenght). 1600 pixels x any lenght is ok, just make sure it's a size your device can endure. If you work on bigger resolutions, just stick to what you know in case you want to print the comic later. I'll recommend doing your comic in traditional book format first since that way you already have it arranged instead of doing vertical format first and then struggling in case you want to print it. To put as an example, you won't like your comic to look like Lore Olympus book version... just having 2-3 panels per page seems... a bit ugly but that's me personally.
Don't rush things: I get you want to tell your story but you'll only stress yourself if you make a chapter and immediatly post it, try to have at least a batch of 10 episodes before publishing, that way you can work and keep a steady schedule
Try to have a draft for your story or a script: I know you probably are going to tell me you have been working on your head this story and you know how it starts, what you want to have in it and how it ends, but try to build up a structure just so you don't end up in a dead end or in clashing against a wall (plot) that may take some turns to resolve.
If you're going to use assets, some free to use backgrounds, pngs: Make sure that the style matches yours, try to use them as guides and avoid your work looking like a collage. While you don't need to be a perfectionist I believe you won't like your stuff to look like this, but you can also have an idea about how relaxed you can be (Yes, this is from Let's Play, an Official Webtoon)
Things don't need to be perfect: Most of people won't care about anatomy or hooooooow detailed and crisp your lineart is, that's usually what other authors will see, but most of readers won't care about those things, they just want their chapter, know what's happening in the story. So don't torture yourself with a panel being perfect and beautiful like an illustration... the more you dedicate to a panel the more they'll ignore it lol.