My advice: write the script and draw a storyboard/guide of a whole part of the story/chapter before actually drawing the pages. Don't work every page from scratch. You're making a long story, and those work much better if you have everything clear before you start drawing. It sounds boring and a bit unnecessary, but trust me, unless you're a script genius it's the best way to get the pacing right. I may not be the best at drawing, but I've written lots of scripts and stories.
For The Lonely Moon I have a text doc where I wrote down every single important thing that needs to happen to reach the end of the story, in a very simplified way (ex: girl arrives, meets boy, they meet x character, this other thing happens, the planet explodes, everybody die). It doesn't have to be pretty or too detailed, you're the only one who's going to read it. It really helps you write each scene if you know exactly what's going to happen next and how soon, or how far you are from a certain important moment. For example, if your character is a happy-go-lucky boy and by the time he meets a certain other character you need him to have matured a bit or something, you'll know exactly how much time you have before the meeting and you can pace the character development accordingly.
Whit that file all nice and ready (not really nice, you'll change things, move them around, add things, remove others, it's a changing text file! But the main skeleton will ideally stay there), you can start writing the script. You can do it movie-style and just write the dialogues and explanations of what's going on (again, only you will see this so even if you write it terribly messy as long as you understand it it's ok), or if you want to have better control, just draw a really rough storyboard. But don't do it page by page, do the whole chapter or at least a big group of pages (10 or more, for a really long story).
I used to just draw every page without much previous planning for my earlier comics. It works, but on the long run it gets messy. And you suffer stupid writer blocks more often. I started working the way I just mentioned when I started translating my works into English; since I needed help with the translation, I got used to writing whole chapters and then sent them to my translator and/or beta reader, to give her time to work. And what do you know, it helped me too.
Maybe you're already working with storyboards or scripts, but I really suggest having the big skeleton thing written down too. Even if you already know your whole story and everything that's going to happen. Trust me, it's really different to have it only on your mind than seeing it all written down in order.
Hope it helps somehow, sorry for the lame English