I try to find a song I REALLY like that no one has ever heard, and I plagiarize it.
Kidding aside (and great question by the way), my creative process varies in some ways, but certain things stay the same.
Melody is vitally important to me, but so are chords. Typically I start with a chord change I like and let the melody be born out of it. I'm a bit of a 'thinker' in that regard, so when I have a chord progression I like, I typically am aware of the countless other songs that use the same progression. This doesn't bother me, as it shouldn't. But I will often try to find one thing I can change or voice differently to make it my own.
I also often have a model of a song I like I may be patterning after; but genre is not important. For instance, I love the work of producers Mutt Lange and Dr. Luke, and while my little instrumental ditties will never have the marketability of their work, I strive to be as concise in my parts as they are.
Some songs I build the entire rhythm track from scratch with only a rough sketch of what might go on melodically. However, my current song I am working on (which is taking forever!) I am working on all parts simultaneously. I'm hoping because of this when I do finally start recording, it will go quicker.
Some musician friends scoff at building a track without knowing the melody, but not only are many hit songs written that way, I do have a sense of the 'straight line' I want to achieve from start to finish.
Since I record all the parts myself, I do countless run-throughs so I can get it as live as possible. It is my goal to record the parts as if they were played live from start to finish, not punching in sections. I try to limit the number of takes to 3 or 4, but it's usually 5 or 6 (and has been up to 25!).
Then I edit together one good take, do crossfades if necessary, and yes I may even quantize.
But to be more concise for me, it's usually:
1) find chord change I like
2) determine a 'feel'
3) find basic drum loop that fits
4) put together structure, for me usually typically pop song structure
5) MELODY!
6) add drum changes and fills
7) practice parts
8) record parts
9) mix
10) not listen to the song for a year since by this time I'm sick of it!