There are a lot of elements that go into making a good comic, art, story, dialog and, if you can't tell by the title of this post, characters. Creating a good character is actually a pretty tricky proposition, and it's even harder to try to tell someone HOW to make a character without rattling off a long list of "don't do this" and "don't do that." I think the reason is that it's easier to make and pick out bad or boring characters than it is to make a good one.
So I tried to come up with a list of what to "do" when creating a character and it is VERY hard to do without saying "don't do this" in the same sentence. I probably failed at that anyway, but let's take a crack at it. And no, I didn't start everyone with "do." That would be silly.
1.) Characters should be distinctive. They need to be easy to identify in some way, and be able to separate them out from the rest of the cast. With comics, the artwork can do much of the work here, and if you want some more details, go read Indistinguishable from Magic, the blog from the artist of Dresden Codak for more. He's got pages of it. That's not the only way of doing it, the character's dialog and speech patterns can help as well. The important thing is to make it easy for the reader to pick out a character without knowing anything else about them, even their name in some cases (though knowing the name helps, a lot). There are some pitfalls here, but I'll cover them next time.
2.) Characters should have a motivation. Everyone has a goal or desire they wish to fulfill, and these should direct their choices and actions throughout their lives and the length of the comic. Sometimes these decisions and actions will seem out of place and that's fine, as long as the character has a reason to seek it out. The more rash the decision or action, the better the explanation for why the character did it should be. The best part: one character's motivation can power entire storylines, or even a whole comic.
3.) Characters should grow. Static characters aren't a bad thing, but they are boring. Just flip open your daily newspaper and read the comics and you'll see a massive cast of static characters, many who haven't changed in any significant way in decades. As the world in which they live changes, the characters should change with them. Some are going to react poorly, but that should be natural and to be expected. Growth also means letting characters go, whether by sending them away or by killing them, as long as it's done with purpose, it adds to growth.
4.) Characters should have flaws. Now that might sound like another way of saying "don't make the character perfect," but that's not the case. When one is told that phrase, they decide to simply pile on random flaws to the character, often without thinking how it works with their personality. Flaws, real flaws, have meaning for the character in some way. Let's go back to the motivation thing, what prevents the character from achieving their goals? It could be a personal flaw, and a goal to overcome with growth in some way. Good flaws can make a character memorable and possibly make a comic great.
Short list, and I'm sure I could think of more, but not without crossing the "don't" divide. So I guess I'll cross the line for next time, hopefully. See you then kiddies.