"Even in the best of times, being a creative person of any sort is an iffy proposition." Matt Madden
Anyone interested in sequential art should make a first port of call at Scott McCloud's Understanding Comics but for more nitty-gritty Jessica Abel & Matt Madden have two sizeable books: Drawing Words & Writing Pictures and the recently released Mastering Comics (both published by First Second). The books benefit from having been honed through the authors years of teaching illustration and are therefore pretty exhaustive from line technique to character development to both hand and computer colouring and much, much more including assignments. The reason I mention it now is that over on TheComicReporter Tom Spurgeon interviews both Abel & Madden at great length (see here).
"I think that this is one of the problems with comics literature
education now. Not a lot of the teachers are equipped to talk about what
the images are doing. They can talk about plot and character and all
this good stuff., but are they talking about how the image composition
actually tells the story? And that's what this is: that's what this art
form is." Jessica Abel