If there's one thing that can be hard to get a feel for early on, it's pacing. Knowing when to go full steam, when to ease up and let a story breathe, when to reveal a big twist, and when to just end on a cliffhanger. You're going to screw it up, no doubt about it. But, as with most things in life, you learn by doing. Each story is different, but here are a few basic things to keep in mind to help the flow of your story.
What is your story about? What are you trying to say? What do you want out of your characters? These are all questions you should be asking yourself when you plan out a story. Once you have the answers to these questions, you can begin to get a feel for the pace. You'll probably have a few key scenes in your head, and you can start figuring out where you want to place them. Try shifting them around a bit and see how things flow. Sometimes your first instinct is right, and sometimes something that might feel wrong to you, might actually be the best thing for the story. It's just trail and error. You can always change things back.
I'm sure this isn't news, but that first page is really important. It sets the tone for the rest of your story, and hooks in readers. Now depending on your story, sometimes this means starting out with a bang, and sometimes it means setting a certain mood. So make sure you put a lot of thought into how you open things. Again, if you don't like the start to your story, try swapping it out for another part and see how that feels.
A trick a number of writers use is to end each page with a mini cliffhanger to make the reader want to see what happens next. This could be someone asking a question, or maybe a character makes a shocking discovery, or a fight is just about to break out. So take a look at how you're ending each page. If that last panel doesn't make you want to keep reading, you might want to change it to something with a little more punch.
Sadly, the cure for exposition still hasn't been found. It's something you just need to work around, and that means like a parent trying to get a picky kid to eat, you'll have to make it more fun than it seems. Going back to Brian Michael Bendis and his work on Alias, there's this running gag of Jessica sitting and listening to a client as they tell her the details of a case. These where often two page spreads with the same image of Jessica repeating at the top, and the client going on and on the bottom of the page. Here's another example:
Having this as a running joke in the series helped spoon in a lot of that exposition, but a lot of it comes down to how well your artist does with acting and subtle emotions/body language, and not many are as good as Michael Gaydos. So instead, if you have a scene that you need to get in with two characters just talking, try and think of exciting things they could be doing or places they could be. Different medium, but on The West Wing, Aaron Soarkin would often have characters do "the walk and talk." Having important conversations happen on the move would convey a lot of the energy and sense of urgency going on in the White House. So if you can have your characters moving, flying, fighting, driving down a spooky highway, hanging out in a funky bar, anything that isn't just two people sitting down talking in a vacuum, do it, because nothing can kill the momentum of your story like a long and static conversation. No matter how pretty or dramatic your words are, it's still a visual medium.
Speaking of visuals, this is when that panel discussion comes back into play. There's something about having a similar panel count on each page that gives your story a good rhythm. Again, most people try and keep it somewhere between 5 to 6, but there are plenty of stories that obviously still work breaking out of that mold.
A quick reminder here about how the panel count can effect the reader. A page with a low panel count tends to move a bit quicker, although it's possible a reader will linger on the bigger panels. A higher panel count will slow a reader down, having to take in more information.
So lets begin with the Miracle Man story "Skin Deep" By Neil Gaiman and Mark Buckingham works almost entirely on a two panel grid, like this:
This gives the images plenty of room to breath, and Gaiman plenty of room to work his usual magic. The advantage is obviously the space for you and your artist to tell a story, the con is that you then have a limited number of panels to tell your story, so you have to choose carefully.
Then there's also the 9 panel grid which was most famously used to great effect by Alan Moore and Dave Gibbons in Watchmen:
This is definitely on the opposite end of the spectrum from the last example. 9 panels gives you a lot more space to deconstruct a story and pace things out. The trouble you run into with this is the amount of work for an artist, and can give your book a bit of a static feel. Not every can pull it off well, so make sure you have an artist comfortable working with 9 panels.
Finally we have comics that don't really fit into either of those categories:
How many panels would you call that? Again, you don't run across many J.H. Williams III, so artist like him and Marco Rudy fall into a category all their own. The key is to make sure the reader can still follow what's happening and not get lost navigating the art.
A few final notes. Don't feel like you need to force a crazy action scene into each book. There are plenty of ways to make your story compelling without fist fights and explosions. So don't panic if you finish a script and realize no one got punched. An issue leading up to a conflict and can be just as compelling as the conflict itself. Also keep in mind the different ways you can structure a page to break things up. A silent panel will cause the reader to pause for a moment. Short, back and forth dialogue will speed things up. Similarly a bigger panel will immediately grab a readers attention, while smaller panels and inserts can be used to get across some quick information. So just keep in mind all of your options when putting together a page.
Lastly, check out a few of these writers for great examples of pacing. Obviously Alan Moore with Watchmen but also From Hell. Matt Fraction and David Aja's Hawkeye run. Brian K. Vaughan and Pia Guerra's Y: The Last Man. Peter Milligan and Mike Allred's X-Force/X-Statix. And of course Neil Gaiman's Sandman.
I could go on with those forever, but I'll stop there for now. Take a look at your scripts and comics and see what you can do to improve your pacing. Maybe change the way your book starts, or some of the last panels on a few pages. Next time, I'll talk a little about every writers favorite/least favorite part. Dialogue. Until then, go make some comics!