Comics exist at a really cool cross-section of sequential visual media and written.
I think the three biggest things about comics that need to exist to make them "good" are:
- Legible text
- Legible art
- Making it very clear how the reader is supposed to read through a panel/page
Those are the barebones basics in my eyes. The story and art can be rough as hell, but if people struggle to even understand what they're looking at then it just can't be read. Consider studying topics like composition and flow. Many people have written about them many different ways online, and once you learn the basics you'll start to pick up on how they work when reading the work of others.
When it comes to writing, I don't consider myself a super practiced story-teller, so I think I fumble around a lot too. I recently found this cool blood post here that is targeted directly at how to write a graphic novel, so maybe give it a read! And just from personal experience, I say to try to have a decent grip on your whole story before you start if you are looking to tell a story with an ending. Otherwise you either are going to go forever, or just write yourself into a corner.
If there are any more specific things you want to talk or ask about, totally let me know!! I'm pretty passionate about comic creation, so I've got resources or at least advice about most things. (. ❛ ᴗ ❛.)
Good luck on your comic-making journey!