I say.... do it how ever you want. There are no "panning" rules in mixing that says a solo instrument must be at 12 O'clock. As a matter of fact, unless it's a vocal, I rarely put any instrument at 12 O'clock. Put it where you want to. Listen to an older Van Halen record. The lead guitar is way off center.
For normal rock-n-roll, jazz, etc (non-electronica), I like to listen to the song, decide on the vibe, and then mentally put together a stage or venue in my head. Then, I lay the mix out accordingly. I pan the instruments how I envisioned them on the stage, I set my reverbs, pre-delays, etc to approximate the room I see in my head, etc... I'd say that's how I mix 90% of the time... the other 10% I do whatever... depending on my mood.
There are no rules...
-Tom