there's a lot to be said for using what others have done before as a reference point. It's not that you're trying to copy or sound like, but rather having a benchmark for what's a great _________.
I listen to different CD's/artists, for different instruments, as well as different genres. Example, I like the sound of McCartney's bass for certain styles (and really not much of anything I write/play is very 'Beatle-ish"), for something else, I might listen to Sting. For guitar's... acoustic - James Taylor, Dave Matthews. Drums- Fleetwood Mac and much of Clapton's music. Electric guitar... wide open here...and here's where I tend to "go-it-alone" (I'm mainly a guitar player, so I go for a recorded sound/tone that keeps me from thinking I need to buy another amp/guitar... not that it wouldn't be fun... but) Vocals- lot's of folks, butt if I'm working with a female vocalist, I'll listen to Aretha, Sheryl Crow, Chrissy Hines, and anyone else that's similar in sound to the vocalist I'm working with. Male vocalists- Dr. John, Leon Russel, David Byrne, Dave Matthews, Michael Franks, Jack Johnson... Keyboards is more about what kind of keyboard. I have a Hammond M3, a Rhodes 88, Yamaha S08, PolyKorg, and a Farfisa professional, so it comes down to "what sound do I want"? Even the keyboards themselves serve as a reference.
and there's just listening to entire pieces to study how everything is placed (panned) and the arrangements and how the piece transitions through the various parts of the song.
And again, I'm not specifically trying to emulate any of these other artists, just get a mental image/sound in my mind that I'm after.