Rosalind has the ability to rise above her own deeply felt emotions. Her love for Orlando makes her feel as giddy as any lovesick adolescent. (Look at her excitement when she learns that Orlando is in the forest.) She could easily surrender to the temptation to run around reciting poetry and swearing to die for love. Instead, she administers a love cure to Orlando that makes both of them stand back and take a good look at how ridiculous many conventional attitudes toward love really are. Thus, she avoids confusing the "idea of love" with love itself.
She is also remarkably clever. She makes up the love cure on the spot and quickly invents an uncle and a magician to justify the stories she tells. And she's practical enough to be sure that she and Celia acquire a place to live as soon as they reach Arden.
Rosalind is a good judge of character. She appreciates the skill of Touchstone, the court fool, and immediately sees through the pretensions of Jaques, Duke Senior's melancholy attendant. She has only to observe Silvius and Phebe for a few moments in order to size up their situation accurately.
Finally, you should take note of her courage. She boldly tells the usurping duke that her father was no traitor. It also takes spunk to go on a dangerous journey disguised as a man because highwaymen would probably attack the man first.
Celia
In Act I, Celia has just as much to do and say as Rosalind. She fades into the background, however, as the play goes on. Although she remains undeveloped, many readers find her a charming character. She and Rosalind share a deep, loving friendship, and her importance is a function of that relationship.
First, she serves as a confidant, a person with whom Rosalind can talk openly about her feelings. While Rosalind hides her true emotions in her scenes with Orlando, she is absolutely honest with Celia.
What raises Celia from dramatic device (someone serving merely to help the play along) to a character who is interesting in her own right is her wit. From their first appearance, Celia matches Rosalind in her ease with words. Since Celia doesn't fall in love until nearly the end of the play, she also retains her cool judgment. Thus, when Rosalind expresses her own romantic feelings, Celia is there to undercut them with pointed jests.