There are a thousand things to hear about, informationally, daily, but the thing that doesn't go away is the one to pay attention to.
Teenagers, especially girl ones, seem like the perfect canary-in-the-coal-mine characters to me. They capture American culture and its perversion, its hypocrisy - how absorbed we are with youth and beauty and sexualized imagery, for instance, while preaching abstinence and modesty.
My father was among the first of his generation to look into writers who've become part of the American lit. canon. When he wrote his master's thesis on William Faulkner in the Forties, he couldn't find anybody on the faculty at Columbia University to oversee it because they didn't read Faulkner.
I like the way that psychological extremity can illuminate more 'normal' characters by forcing a comparison.
I guess the thing I would say most fervently is that your original impulse to write something is an impulse you should trust, and that if it doesn't work on the first draft, which it hardly ever does, the commitment to revising ought to be something you embrace really early. And to revise and revise and revise.
The most enduring battle is between head and heart; what would be efficient and logical is nearly always trumped by what is messy and illogical.
Empathy is not as complicated when you have some aspects in common with your character; it's not impossible to know someone who's like you in many ways but different in one. This is true especially if you are a reader. Reading makes you accustomed to inhabiting other lives and sensibilities.
I'm a little hesitant to make my characters sentimental or to risk having the work labeled sentimental. It's something that I resist as a reader, and I don't resist it in life. I'm not an unmoved person by any stretch, but I think I don't want, I guess, to indulge those kinds of things sometimes in fiction. I can't tell you why exactly.