@mojobone... you know you never "steal".. you "emulate"...
I would agree with mojobone that the easiest way to write a "popular" song is to dissect the popular songs out there. And with knowledge of music theory, it's easier to hear and undertand the impact of certain chord changes or having one melody over another with the song you are reviewing. Many good bands are trained musicians, other just grow a good ear, either way the good songs tend to funnel down to certain theoretical conclusions that are appealing to a general audience.
My best cheats are to listen to one artist, take a rhythm from one, chord changes from another and emulate certain melody style (fast, slow, stacata, twang, whatever) that gives that artist their "sound" and put it all together to make a song. Then I'll get comments of "That sounds a little like so and so" but the tricks I used are so distance from the original that it simply sounds like a good popular song that the artist in question might wish to sing. This works great for when submissions are asked for in a certain style.
There's good suggestions on here for books and certain lots of online subject matter, but the main ingredient is that most pop songs in any genre have a positive feeling. Even in a song about dying for instance, "Live like you were dying" , its about a man dying is uplifting with a spiritual feeling of hope to it.
One great rule of thumb, and I've forgotten whom I should credit this to (not my idea), is to always write the song to appeal to women. Dont' write a song that would insult a woman. Whether the singer is male or female, the best all around appeal is a song that a woman feels good about. Even if you write a male-bashing song, women will mostly like it, but even then, write it with a purpose of why this certain man or men are bad as opposed to most. That will gain respect from both genders.
Keept it general, not too specific and you can write a CD full of songs for the next American Idol.... i.e. songs about emotions that reach a general audience: love, angst, rebellion, coolness... and NEVER about hate unless its catchy, kitchy or funny such as Miley's "7 things". Specific songs (referencing a city, a storyline about mill workers, or personal preferences.... like "Santa Baby" since we're in the season....) usually tend to stylize the artists, if you're writing for one person.
I wish I had your education and talent, but then, you could benefit from teaming with someone who has written some good songs but needs tweaking on getting that emotional hook from having some good theory applied to the music and melody aspect of his/hers song.