There is really no "proper way" to pan it. I would ask them how they usually play live shows and go off of that. That said, there are some guidelines I might follow.

Place the drums pretty much in the center of the mix. For jazz, I would pan the kit as you see it in the studio.

The rest depends how the other instruments are played. If the pianist plays a lot of chords in the low range, It will conflict with the bass, so make sure they are spread farther apart. If the pianist plays a lot in the mid/high range, and so does the guitarist, then they must be spread the farthest apart.

However, most likely the guitarist is the frontman, so put him in the center in front of the drums, or slightly to the side. Then put the piano and bass panned farther apart. Don't be afraid to ask them how they want to hear themselves, or how they usually hear themselves. It will help you, and save time for both parties.

-restashured

in my experience, lower frequencies loose most of their punch when panned from center. I keep anything classified as "bass" mono.
Other than that, pick up the Spin Warp 3D panner and automate everything all over the place and give us all motion sick-ness!
jk.

thanx man