Hey man, I'm no expert songwriter myself. But honestly, the thing that makes a song good more than anything is the melody. Catchy chord progressions with a 'stuck in your head all the time' melody is what you want for POP music.
I'd suggest starting out with chord progressions first and writing melodies to fit them. Then, as you get the idea start writing melodies first and making harmony/chord progressions to fit it... Not sure how much you know about music, but you really gotta know at least a bit to write melodies and chord progs...
As far as lyrics go man, it's whatever pops into your head when you hear the melody. sometimes the lyrics come first too. it depends. I'm pretty terrible at writing lyrics so I can't help ya much...
Hope this helps you a bit...
happy writing