1. Nobody likes Nazi Medic
2. Not everyone likes femme classes
3. Nobody likes your teenage sparkle desu class
4. Nobody likes your female sparkle desu teenage class

A lot of it comes down to preference, but a few things keep common themes. These are in no particular order.

It's probably best to avoid stereotypes and overused concepts (not naming any, but if you watch for long enough, you'll see them.) While they can still be done well, they're pretty likely to make people gloss over the character without some seriously unique characterization to make up for it.

Focus less on what they are and more on who they are. A less commonly depicted nationality or ridiculously heavy accent written phonetically doesn't really add to the character and can actually detract. Similarly, mental and physical ailments are not to be used as quirks or gimmicks and that can turn out to be offensive if the illness is misrepresented.

Give them history that explains how they came to be who they are, why they are their class, how they obtained that set of skills, and how they came to work for their respective company. Even if you don't make it public, it gives you a better grip on the character and that kind of consistency tends to help more than anything else ever can.

If they seem out of place on a team that kills for a living, they're probably going to be written off as a self-insert or porn doll. This is especially so if they're women with pinup bodies, overly shy and stuttery, too young to realistically have enough experience to be effective as their assigned class, etc.

Know the time period you're writing for and try to avoid anachronisms. It isn't necessarily 1968 that you're writing for, but this certainly applies for any setting other than present and period inaccuracies are another fast way to turn people off to a character. (Some common ones for the 60s are pierced and tattooed people with no connections to any subculture that utilizes them, openly gay men who've experienced no violence for that fact, and women in combat positions in the US military.)

In summary: write them well, make them storied and engaging, and know the character. I hope this made some marginal amount of sense.

No matter what, you should always think of your characters as people. The problem with most of the artists on dA is that they don't think of their characters that way, but more as vehicles to live out their own fantasies. They're most concerned with how their characters look and how powerful they are, and more often than not whose pants they wind up in. You should be concerned with a character's story and development as an individual, and his place in the overall storyline you're participating in. Oh, and having fun too of course.

>>1769
This is pretty solid advice. Allow me to expand on it a bit.

>Similarly, mental and physical ailments are not to be used as quirks or gimmicks
This is really important. Give your characters actual personality flaws. From what I've seen of OCs/Roleplay characters in general is that some people think if they give their character a mental illness or physical handicap (usually improperly represented or written) that makes their character unique and deep. Especially when lazy or incompetent writers give their female character's backstory rape for cheap drama (that one is really prevalent, unfortunately). It really doesn't make them more interesting, and is often insulting and offensive to real people who have suffered through those problems (as well as marginalizing their experiences). Real people have both strengths and weaknesses. They'll overcome some and still have others. Allow your characters to get into bad situations. Let them get hurt, get into arguments with other people, make enemies, and maybe even let them die (if the situation is appropriate).

When writing their backstory, think of how their experiences shaped their personalities, and how their personalities shaped their experiences. Someone who is outgoing and extroverted during their youth will have a different experience than someone who is introverted and shy, and even two people with similar personalities will have different experiences depending on where, when, and how they grew up, and they will be unique from one another because of that.

Also, keep in mind experiences that shape a person are not always bad. It might be hearing a certain type of music for the first time, or reading a certain book, or meeting a certain person, or visiting a certain place. No one's life is perfect, but having an overly-tragic backstory just makes things melodramatic and silly.

>they're probably going to be written off as a self-insert or porn doll
Keep in mind that this can be done with male characters as well as female characters. There are just as many bad walking necrophilia stereotypes as there are big tittied barbie dolls, and both are just as creepy and pathetic as one another. There's nothing inherently wrong with having an attractive, or gay, or female character, but when that's all they are it becomes painfully obvious that the creator was thinking with their genitals and not their heads.

When it comes to the setting, you actually have quite a bit of wiggle room for TF2 OCs. Yes, the game does take place in the 60s, so there is some level of the plausibility, but you should focus more on fitting the plausibility of the TF2 world. It's a very crazy, over-the-top, humorous world, but it does have some limits. You would need to consider the tone of the story you're looking at. A serious or dramatic storyline would warrant a more realistic approach, but a humorous one would allow for the same level of in-game silliness.
That said, a 16-year-old, 90 pound, half-Japanese 10th class is never a good idea.

All of this is extremely relevant to stuff I've been too pussy to ask about.

While I'm not new to making OCs, role-playing, or anything like that, I guess I'm still a total greenhorn when it comes to the TF2 fandom.

So I'd like to make a female OC, a BLU "Scout" at that. She's supposedly Scout's sister or something to that effect. All I've really worked out is that she wants on the team, but obviously can't, being female.

Does that sound like something that wouldn't make people rage at me?

>>1777
>Scout's sister

>>1777

It's generally frowned upon to have an OC connected with any of the canon characters, especially when they alter the established canon for that character.

Good point. For some reason I seemed to have forgotten that... (Scout's background that is)

>>1780

The other thing about having OCs connected to canon is that unless the connection is really esoteric and open to interpretation, it creates potential for clash with others who may (and do) have the same idea. Those characters may have trouble existing in the same space and it's better to just avoid a situation like that altogether.

>>1780
And, while they arent frowned upon, female OCs tend to get a lot of trouble.

Mostly because they tend to turn into Mary Sues or self-inserts and make a huge deal of their gender everywhere they go.
There are some well done ones, and Im not saying your's isnt, but Im just warning you that people might not like that.

Hrmmm true. I don't really use her for anything important.... More for eh... random input and occasional narrative... This is the OC in question by the way ....
http://withdanger.deviantart.com/art/Let-Me-Show-You-My-Bird-271497357

....and yes I know avian flu didn't exist in the 1960's.

>>1783
Well, I don't really know much about her personality, and since we've already warned you about making connections to canon characters, she seems okay. Nothing in the design jumps out at me as being Sue-ish (looks pretty sensible). The fact that she's not wearing a miniskirt with her boobs hanging out already puts you way ahead of most of the competition.

>>1782
The TF2 fandom seems to be pretty polarized on issues surrounding OCs and even genderbends. Some are staunchly opposed to both on pretty much all occasions, others embrace it fully. But other anon is right, people's guards go up way more when there's a female character involved. So just keep things sane, think them through, and keep a sense of humor about things. I would avoid the standard "CANON CHARACTER FALLS IN LOVE WITH OC" storyline, however. That can be found in any fandom, but gets pretty bad reactions in general.

OP here to finally thank all of you who helped me out with this. I've made my character more of a background character instead of 'part of the main team.' She's more of a working behind the scenes character and believe me when I say that the only time she will be with anyone is if someone asks me to. IE: Never.