She has to have flaws. And she has to overcome these flaws. And, really, this definition could be (and is, in my mind) broadened to all strong characters in general. If a character is strong from the start, I can't invest in her. I have to live vicariously through her as she comes into possession of her strength. After all, we don't read books for their ending! (Well, I don't!)
I like it when the female lead knows when to ask for help, but isn't a helpless victim of circumstance. Resourcefulness, intelligence, strength (physical and/or mental), ability to love, and a willingness to fight when necessary are key components. I also like a woman who is capable of love. So many strong females put that aside. I like when she can find just the right person to complement all of her strengths if the story allows for romance.
I like characters who are special because of their own strengths--not because of some prophecy, or incredible beauty, or something cliche like that.
There are a lot of characters who, despite being strong heroines, annoy the heck out of me. Miriam/Mirya in Gael Baudino's Strands of Starlight comes immediately to mind. The flat characters with one-track minds.
Personally, while I love strong women who take on men on their own terms and beat them, my favorite female characters are the ones that are so confident in themselves that they don't even need to do that. Phedre in Jacqueline Carey's Kushiel's Legacy series is one of my faves because while there is plenty of sword fighting in the books she accomplishes her goals within her own skillset -- her skills as a servant of Naamah (yes, a prostitute, but in this world that is an article of faith); her skills with languages; her ability to listen, analyze, and reason. She keeps Joscelin around to do the physical fighting while she goes about saving her country and the world. :)
All of Lois McMaster Bujold's female characters function the same way. Cordelia, for instance, can win the same way the boys do, but she despises their insistence on physical strength and their valuation of a soldier's life as the only honorable one.
I totally agree with your assessment of Phedre. I think that was a really great idea of Carey's - to have a character who has certain skills that might not be what the mainstream reader wants to identify with. HOWEVER, she uses her head AND her body to get out of situations. On top of which, she's loyal to 'her' people: her family, her love interests, etc.
See, most of the time good female charicters are best but everyonce in a while I like a bad girl. Without anyone bad the story is boring, and sometimes the one made out ass the bad one is not always bad, some times it depends on perspective!
In terms of great female villains, I think the best I've come across is Melisande Shahrizai in Jacqueline Carey's Kushiel's Legacy series. Brilliant, beautiful, and utterly amoral. :)
I have found that a strong female character acting from the position of submission to be very empowering. It allows strong femininity, intelligence and strength of character to be expressed without the necessity of a woman acting as a man. An example is the character Ellíséyan in Amber Carez’s book, The Hunter. Do you know of any other books with that sort of strong female character?
With the idea that you can be stronger by submitting than by fighting? There are a couple books by Susan Wright: "To Serve and Submit" and "A Pound of Flesh" which deal with a submissive woman - be forewarned, there is a lot of sex.I read the first one and was intrigued by the concept, but I found I was uncomfortable with it. Mostly because I like my 'strong' female characters to be more like me, I suppose: loud, impulsive and weird. :)
Well, there's Jacqueline Carey's Kushiel's Legacy series, mainly the first trilogy featuring Phedre. She's a sexual submissive by divine fiat -- her god made her feel any pain as sexual pleasure, for philosophical purposes that the series spends almost 2500 wonderful pages exploring. ;) There is, obviously, a fair amount of sado-masochistic sex with Phedre as the submissive one, but I find Phedre to be the best heroine I have ever read, because one of the strongest through-lines in the book is that idea that that which submits is not always weak.
There's also Octavia Butler's Wild Seed, which has significant overtones of an abusive relationship but handled absolutely beautifully.