Since I don't know where you're having troubles, I'm going to go in depth on this. So like, forewarning, you asked for this.
Conception
Before drawing, before even writing, I throw ideas at my editors (they're just my friends, but they put up with so much of my shit they honestly kind of deserve to be paid.) and brainstorm.
Then I take what's working, and start expanding upon it.
I'll start by just writing out an event that I want the story to get to, and I'll just have fun with imagining the dumbest/coolest shit I can think of.
From there, if it's still working, I'll actually just think about it a lot, whenever I'm not working on it. Driving, working, eating, whatever.
The important part is to daydream the scene as much as you can, but not in a lackadaisical way.
You're doing this to play out the events you've been formulating, and tweak what you to keep, rewrite, and just axe.
Script
Then I script. I do the entire chapter's ahead of time, before I even draw a single line for a page.
The way I have the script set up, I nest the lines in such a way that I can just run my eyes down the edge, to jump from panel to panel.
Each > here is a panel. Anything indented is a bullet point describing it.
Subsequent indents describe the prior bullet point. So on and so forth.
6 to 8 panels is a generally good number. You can do more, you can do less, but six to eight is good. I'll explain why in a bit.
Thumbnailing
From there I thumbnail.
The screenshot of it here is 100% size on the canvas
The small size is integral, it allows you to see the entire page in your focal vision, and you're able to tweak everything way more easily.
I determine the layout I want for the panels
Layout
Panel layout is something with a crap ton to it, that you'll have to ask me to make another post if you want me to go in depth on, since it's got so much to it.
But in general I find that three rows works the best for anything you're doing. It's the most visually appealing, and also lets you cram in the most "comic" for the least amount of work.
You can find a multitude of templates online, I'd recommend a manga template, they're the most neatly layed out ones, and western comics tend to just do whatever with their panels.
The way you determine layout is gauging what events you want to put on the page, and what panels should go where. Sounds like I'm over simplifying it, doesn't it?
It seems harder than it is. It's a matter of picking the "keyframes" to it, in order to best convey the sequence.
You want it slower? You include more keyframes in a shorter amount of time. Faster? The opposite.
When you've got those, you take a chunk of 6 to simplify.
In your head, divide the blank thumbnail into 2x3.
Now you increase and decrease the size, based on importance.
Need more panels? Just stick one in between any of the rows.
There's a lot more to it than just that, but those are the easiest rules you can follow, and it'll all work out decently.
I will add one more thing though, pay attention to your gutters. Time passes between them, so the bigger they are, the more that does, and vice versa.
By proxy, you can use them to "group" panels, and make it easier for the reader to go from panel to panel.
Wrap up
That thumbnail is then copy pasted onto the page template, scaled up, and lined up with the margins of the final page.
From there, it's sketched on, inked, colored, and given the finishing touches.
Keep in mind, I'm never locked in at any point in this process, but the further in I go, the more work it'll take to change something. I actually jumped back a page, to provide all these examples, because of how easy it is to change shit. And my script, thumbnail, and sketches, didn't line up.