Some cliches can be stopped. To help you avoid cliches, here are the Top Ten Worst Offenders:
10) Vampires. They're dark, angsty and supernatural. Perfect for artists that are trying to explore their dark sides.
Unfortunately, few think vampires all the way through. They look at the angst factor, mostly the night-onnly existance and the parasitism, but not the advantages of being a vampire. Once you get past the need for blood and darkness, you don't have to pay taxes, the money you were paying for most bills and food becomes disposable, and you can concentrate on what makes you happy. Okay, so you can't have kids either, but that's sorta plus/minus.
On the flip side, there are those that try to find psuedo-scientific reasons for vampirism. Obligatory: Huh? They haven't thought one major thing through: Vampires only work when they are mysterious, and they end up not working as well when their secrets are grounded in reality. Not saying you can't do it; just be aware of the problem.
If you are going to use vampires, don't get drowned in the angst, and consider that they would revel in their advantages (such as their heightened senses, the ability to pursue things for a longer period of time, and immmunity to a wide variety of things). If you can't, just remember that not enough people use werewolves.
9) Collector Comics: This is a corporation's favorite: A comic with a built-in collectible. Although there's only two major offenders (Pokemon and Yugi-Oh), there are a lot of minor ones (Digimon, for example). However, it goes far behind just toys.
The basic idea is that a hero (or group of kids) are looking for a group of objects or animals in order to solve his (their) quest. Although great in that success is measurable, and tension is guaranteed to mount with each piece collected, it starts getting monotonous as battles start to mount, especially if every fight is the standard "old trick gets negated, hero almost loses, finds a new trick, wins" formula.
This is great if there are just a few pieces (Dr. Who's Key of Time only had seven pieces). But there's a reason it works great in games, and not so great in comics: Each goal accomplished limits the time left. However, try to avoid this one unless you have a good reason; the reason that it's on this list is because (besides being used a lot) is because too often authors use it as a crutch (by setting measurable goals, you feel good when you have accomplished one, and feel better if you know the path has been that much more finished), and there is the temptation to add/reveal "just one more" collectible.
If you can keep to the objects that you have revealed, and have fun with it, go for it. Otherwise, avoid like the plague!
8) Magical Girls: I'm not trying to be anti-feminist, but heroic girls set the feminist movement back by ten years each time they show up. ("Super-Sailor Charon, let's defeat Masculinor and then go to the mall! Magnifence Cherry Beam of Cheeriness!"). Yuck.
I'm sorry; this is just a genre that needs to either mature or die. But, since it comes up, how do you deal with it?
First off, make sure that none of the girl's involved are Mary Sues (almost-perfect with special abilities, flaws that are more dramatically appropriate than real, and worry about their perfection). If you do have them, kill some of their specialness, and give them normal issues, not hyped-up petty ones (she needs to defeat the bad guy quickly in order to make a date, not because he messed her hair-do).
Second, make the guys real. I like WITCH because the recurring males are realistic guys, not merely foils for the girls. Even without powers, Caleb (the rebel leader), Blunk (the "pet"), Matt (Will's love), Martin (their fan), and Uriah (Caleb's friend) are just as vital to the fight as the girls, albeit in far different capacities. I could have an episode with just those characters, and it would be interesting. Contrast that with the guys in the Winx Club, who are easily replaceable. They have enough problems just being on-screen; there is no way they could sustain an episode by themselves.
Third, and last, don't try to be feminist. It invariable works against the story. Just let them evolve as characters. I cannot emphasize that point enough!
7) Game Comics: This is not to say that there aren't great game comics. Penny Arcade and Goblins are great examples. However, because gamers tend to be computer literate, and some are decent artists, they try too hard to relate what happens in games to others, and it just doesn't always work.
If you are serious about making a comic based on a game, do up a script, and then show it to someone who is not in your immediate circle. If they think that's entertaining, go for it. Otherwise, just put it down and either try something else, or just do it for yourself and your immediate circle of friends.
6) Conspiracy Theories: Every action has a reason for happening, right? And, as we're interested in looking for reasons behind why things happen, we're liable to assume that if we can't see the reason, then someone made the decision. Most people realize that some decisions are by nature arbitrary; a decision needed to be made, but several options were acceptable, so one was chosen.
Others, however, believe that there is no such thing as an arbitrary decision, and that every decision is made for a reason. The next leap of logic is that the reasoning behind the decisions is part of some struggle, and that there is some sort of war going on, making every decision important. Thus are conspiracy theories born.
A lot of writers like them, as they feel powerless in their own life, and seek to demonstrate this by showing how powerless the average man in a world where all his decisions have already been made. They then make the hero someone who rebels against the conspiracy, proving that there is free will in the universe.
The issue here is that it removes free will from the situation. After all, the easiest way to deflate tension is to make it obvious that any decision that's going to be made has already been made. Think about this for a moment: You have two organizations that have been going against each other for milennia, and they can predict the other's moves.
So, if I belonged to one of the big organizations and I knew someone would be making a choice, and I knew how the other organization was going to react, then why not give him some sort of information that affects his decisions, and then affects his decision towards my preferred result? Thus removing any actual choice, and gaining an ally against the enemy organization because he feels so good that I allowed him a choice, even if he thinks that he's acting against mine as well.
There is the question of whether or not there really is free will, which is rather depressing. The ironic thing is that the writer usually says that he is an atheist because he thinks that God has a destiny for everyone, and that there is no free will. And then he then proves himself that everything is, in fact, pre-destined.
Just pointing out that when you start down the path of conspiracies, you remove a lot of dramatic tension from your comic, which rely on dramatic tension.