As much as most of this would apply when writing a pop song, you can't really tell people how to write their own music, because it's all about expressing your own personal creativity and influence onto an idea. I write music, both lyrically and for five or six seperate instruments and each one is very different from the next, and I always try to make each individual song have it's own special style or 'personality'. But then again since you highlighted a Pussycat Dolls song as being 'well-written' it's obvious we have very different influences and ideas as to what to makes a song good, which is why I'm sort of saying you can't tell someone how to write a song because it only applies to someone with similar tastes to you.