Probably let the piano sit in the centre as it is naturally broad sounding instrument, then the Cello of to one side (left?) and the guitar to opposite (right?) but that is only a suggestion.  Also it only needs a tiny pan 20% max either way I would say.

Thanks so much! That helps.  :) 

I agree...piano center.   Guitar a little left, high strings a little right (so the high freqs will balance with the guitar), cello maybe a little left?
 
Actually, it could be fun to try a little Mid-Side processing to the track and see if you can get a spread of the high strings to both left and right.  Or get wild and try a stereo widener or something similar to those strings.  :-)

Equally good plan Tony to use some Mid Side, if you have channel tools you can use that to create the effect Tony suggests.

Ah, those strings!  Actually that's just 'strings' embedded in my Ivory piano sound.  So I can't really separate them.  But I'll see if I can pan them separately from the piano.  Probably not, but I'll check. Thanks again, both of you. ;) 

well, I had a big long response typed and I hit the "X" instead of a different tab and it's all gone.
 
piano will be stereo output
strings might also be stereo output
 
those two are already panned the way they "should" be, so don't pan them off of center.  IF your "high strings" are violins ONLY, then they should be panned left.  if they include other strings (cello, viola, double bass...) then they should ALREADY be output panned correctly in the stereo field.
 
(NOTE:  I did not listen closely enough to try to figure that out, and I can't get to it from work right now)
 
if you have a cello besides strings, it should go on the right, therefore put the guitar on the left.
 
if you want more info on the why...I'll try to respond again later, but I don't have time to retype all that right now.

Thanks Reece. What I meant to say was those 'strings' are a synth in my Ivory (piano) software, so I doubt if I can pan them separately from the piano.  (And I'm not sure I want to take the time to write a real strings part/s.)  So I was thinking of putting the cello on the right, since that where it sits in an orchestra.  Anyway, so that answers my question. Thanks so much. Sorry you lost your response. :(  

JMO but the piano sounds like every note is a velocity of 127. They're probably not but that's the only way I can describe it.
 
The whole piece sounds kind of mono but other have made suggestions to rectify that.

Very pretty piece Janet and Rik. Sad to hear about Rik, I hope he recovers. Other than panning, I don't think there is much more to be done on this. Just declutter the middle and open up the space a bit and you're there.
 
Regards,
Dan
 

Very beautiful composition and nice playing.  Well done!  I am sorry to hear about Rik -- I always enjoy hearing his stuff on the forum.
It is great hearing you back on the forum and I hope you will be back on it more.