#1. Create a unique heroine.
Many cliché heroines are one-dimensional: the lioness who needs help from nobody or the sack of useless that needs a clue or the nerdy girl who just needs a handsome jock to teach her how to be a lady or the ... [fill in the blank]
The truth is that people--male or female--are multi-dimensional. The lioness should have some hidden self-doubt, the sack of useless should have some hidden strength, and the nerd should have more to offer than what meets the eye. So design a character that is human, with strengths and flaws, desires and motivations, and a certain amount of grit.
Make her human.
I think I like seeing all kinds of heroines - there are hard ass bitches, and weak helpless creatures, and bossy mommys and ignorant aunties in this world and they all need some attention to give a well round world view.
#2. Avoid the feminist soapbox.
With the rise of the feminist movement, many authors write heroines that dance circles around the men. Where the hero fails, the girl steps in and saves the day. That's a bit unrealistic, don't you think?
Men and women make a great team, balance each other out very well. A truly strong woman doesn't need to prove it and isn't afraid to show weakness. There's nothing wrong with accepting help.
Strength and courage do not always roar like lions.
#3. Embrace the femininity of your heroine.
I've known so many women who run from their femininty, preferring to be men. But a good heroine has stage presence, a certain charisma that makes them jump from the page, just as an actress with her feminine appeal makes the movie worth watching.
Feminine means remembering you are a woman and there is strength in that alone.