I've been in your exact position in the past; feeling like I was missing something with my panels, but not really being sure what. There are surprisingly few resources out there. Probably the only book I've read where I really felt like I was learning things that weren't obvious was "Making Comics" by Scott McCloud, which most comickers have already read.
Another common resource you've probably seen before, but I'll share in case you haven't is:
Finally, if you can get a DVD or Bluray of "The Incredibles" to watch the "Making of" stuff about how scenes in that movie were storyboarded and edited, definitely check that out. Anything you can find about storyboarding and how directors choose their shots is valuable.
One of my favourite videos on how NOT to do visual storytelling and why is this one from Folding ideas on why the Suicide Squad movie is a mess:
And for the opposite side and more comics focus, here's the playlist of Strip Panel Naked's excellent analyses of panelling techniques in fantastic comics:
My number one personal top tip is:
If you can't think of a good reason to make a panel not be a square or rectangle, just make it a square or rectangle. Just like with a movie, keep things like extreme close-ups, very high or low angles, dutch angles (when things are tilted on a diagonal), strongly patterned or novelty backgrounds, silhouettes and novelty effects like extreme foreshortening or fish-eye lens looks for only the absolutely most extreme panels where you need impact.
Other tips:
Putting somebody's face high up in a panel makes them look powerful, especially if the camera is looking up at them. Putting them low down in the panel makes them look vulnerable, especially if the camera looks down on them a bit.
If somebody is right in the middle of a panel surrounded by space, especially if they're kinda small for the panel they're in because it's zoomed out, they'll look lonely and vulnerable.
Putting somebody standing at the side of a panel looking towards the opposite side makes it look like they're about to move that way, while putting somebody standing at the side of a panel looking towards the nearest edge makes it look like they have just moved across the panel.
Diagonals always make things interesting. If your work feels flat and lacking depth, it's usually because there aren't enough diagonals. Running directly towards the reader can look flat, so try having them running on a diagonal as though they're about to run past the reader. Standing straight on often looks flat and dull, so try putting the characters standing on a diagonal.
If a character is pointing or looking intensely to the left or right, the reader will follow where they're pointing or looking. Use this to direct the reader to the next panel. On a related note, when characters are moving in the same direction as the reading order (left to right in English), the reader is moving with them, while if they're moving in the opposite direction, they're moving against or confronting or jumping out at the reader. Use this to your advantage.
