I just came back from a brainstorming retreat with five other writers (both published and unpublished).
I tend to approach brainstorming like I do synopsis critiquing--I try to figure out what elements could be altered to add more zing to the storyline, characters, etc. the problem is that it usually makes me question or give feedback on the brainstorm ideas, and some people don't like that, they'd rather just have all the ideas at once, whether they're good or bad.
One thing I kept commenting on was cliche characters.
"He's a cliche hero."
"That motivation is cliche."
"Cliche occupation for your heroine."
I'm sure I drove my brainstorming group nuts (at least nobody killed me or threatened to).
But I really think that in this industry, you need to come up with vibrant, unique characters. There are so many great books out there with awesome characters, and as an unpublished writer, you need to make your manuscript stand out from what's already been published.
The best way to police yourself for cliche characters is to read extensively in the line or genre you're targeting. Get to know what's already been done--occupations, personal issues, personalities/archetypes, motivations, backstories, quirks.
I think that for contests, this is key. You're giving the first few pages of your manuscript to an impartial judge, and if your character is fabulously unique, that'll hook your reader.
(A side note: You'll also need to make sure that your character's unique traits come out in the first five pages or the judge won't be as wowed as they could be.)
I seem to see this a lot in the contests I judge--the characters aren't badly written, but they're not unique. They don't stand out, they don't have an out-of-the-box quality to them that makes me sit up and take notice.
Take a hard look at your manuscript--how can your characters be DIFFERENT?