Some games require that your character have a symbol for her warrior form. Check the page to see the specifics- Lumina Senshi, for example, requires that a hero's symbol be a silhouette cut from a circle. Also, check to see whether or not color enters into the symbol. If the page doesn't say, it's pretty safe to leave mention of color out; a lot of games leave the symbol as a silhouette.
DO NOT leave a link to an image without a written description of your character's symbol. At least try to describe what the symbol looks like. Also, don't skimp on detail- for example, if your character's symbol is a snowflake- what kind of snowflake? How many points does it have? Is it intricate, or simple?
Useful Symbol Links: Symbols.com
An index of many symbols that have been used throughout history. Very useful, very popular.
Uniform
Read over the site and see just what's required, if anything, for warrior form outfits. Many games allow you to make alterations to the uniform template; if you do this, make sure you don't go overboard. Remember that the word "uniform" means that everyone wearing it should have some similarity.
For guy uniforms, try to avoid the cliche fantasy hero outfit of tunic, trousers, cape, and boots (unless that's what's required). Check out some historical costumes to see all the different sorts of outfits you can force your guy into.
With villainesses... I don't know who decided they all dress like tramps, but if possible, try to give your evil woman a decent amount of clothing. You don't want them to catch cold, do you? -_^
As for uniform color, check out the profiles of the other characters to make sure you aren't using the same color that they are. Many GMs have provided a helpful list of what colors are taken on the site. One way to lessen your chances of having a taken color is to use different tints and shades- pine green instead of just green, lavendar instead of purple- or more neutral colors, like beige.
If your character has element-themed powers, (a common trait in most of the games I've seen) remember to take a color scheme that makes sense with your character's element. Red, for example, would NOT be a good choice for a character with water powers.
Use a painting program to check to make sure your colors don't look garish next to each other (unless that's what you're going for). Try to avoid offending the artistic sensibilities of your reviewers' imaginations. -_^
If you're playing a villain, for the love of Mike PLEASE try to pick colors other than red, silver, and black. They've been used to the point of ridiculousness. If it's unavoidable, use one, but try not to have all of them together.
Weapon
You don't always need a weapon. Think over your character's personality, as well as her power source (if she has one), and let that help you decide. A warrior with "motherhood" as her power source would be less likely to have a weapon than, say, one with "war."
It's been pointed out a lot- swords are often quite overused. Sure, a sword is a useful weapon, and found all over the place, but it's BORING. The same thing goes for a bow and arrows. If they're relevant, (it'd be rather odd to find a Sailor Cupid without a Cupid's Bow and pointy projectiles, for example) go for it, but if not, try to think of something cooler. Similarly, staves are getting pretty prevalent. Try something less common, like a polearm or some lesser-known projectile weapons. Also, remember that weapons don't always have to be the immediately accepted arms that everyone thinks of. Sailorneptune uses a mirror. Countless video game characters have silly weapons such as umbrellas, books, or even ladles and frying pans. One of my own D&D characters uses her backpack as a weapon- heavy textbooks in a bag make a convenient bludgeon.
If your character uses magic and has a weapon, you may want to incorporate her weapon into the powers in some way. (Many anime-based games actually require this.) If this is the case, mention whether your character can use her magic without her weapon, and, if so, what effects there are. You never know when the enemy might snatch it away!
Thoroughly describe your character's weapon. Don't just say "throwing knives." Tell how many (three? twelve? an infinite amount?), how long they are, what the hilts are made of, what the blades are made of, if there are any interesting engravings on them, et cetera.
Useful Weapon Links:
The Armory
Gi-HUGE-ic encyclopedia of various tools for hurting things, indexed by type. Very cool.