Thats such a broad topic!!
I highly recommend Understanding Comics by Scott McCloud for anyone, whether they're just starting out or they've been making things for a while. It's a great read.
Definitely read this thread! I know its long and text heavy, but its good.
As far as organizing panels, on tapas specifically its good to keep your comic in a mostly vertical format, so that it can be easily read on a smartphone!! Tapas's guide for this is here.
Personally, I have pretty poor vision, so I like to get a few steps back from my laptop and see if I can still read the text, and if I can still see facial expressions. Your faces and your text are your bread and butter! Those two things are the most important, but if I had to pick one over the other, I'd go with faces. Sometimes text can be hard to fit, even after it's been whittled down to the bare essentials. Make sure the faces convey the message the clearest, and from the furthest away. (A good example of this NOT applying is Suicide Prevention Committee, since the characters don't have facial expressions in the traditional way. However, somehow those blank shapes are still so emotive! Its a good read if you're willing to wait.)
Another important thing is that if you use a font for your text, make sure it suits your line art, and keep the size consistent. I do not use a font, but I instead hand write all my text. I prefer this because it fits better with my line art, and I have more control over the shape/distortion of the text itself. Most people use a font for readability, so if you have bad handwriting a font would be much better than hand writing the text.
When you're sketching your panels, keep in mind:
-Size requirements for Tapas and any other places your work is going
-Where your characters are on the page
-Where your text needs to go
-Consistency with previous pages
Block out your shapes ahead of time and take a step back before you start lining. Ask yourself if everything fits comfortably (not too crowded, not too sparse) and if your eye moves along the page easily from important point A, B, C. Flip your canvas and check it again.
OUTLINE YOUR STORY AHEAD OF TIME!!
If you don't know what to draw in the next panel it's going to be extremely hard to keep moving forward consistently.
Outline your chapter summary. Outline your dialogue. Outline your panel descriptions. Outline everything. You can never have enough notes for your future self to work with.
Do not just make it up as you go. You're gonna have a bad time.
Run your story by a trusted friend who wont spoil your comic, but will also give you honest opinions. Share your ideas with them and get feedback to help improve weak parts in your story and to fix inconsistencies or confusion.This will also help when you're feeling impatient about how slow your story is progressing (it will be slow! it takes time!) so you can talk to someone about your story without spoiling it with your audience.
Uhhhh I think thats all I have for now!! I hope these help you on your creative journey!