Yeah Toozey is correct about the solo's and the bass except sometimes if you have two guitarists exchanging solo's you might want to try panning the different guitarist's solos to the same side as their rhythm parts.

If you go direct into your recording device you need to have a realy good amp/ cabinet emulator, most modern guitar multi effects have these, i use a Digitech GNX3 for this ang direct into my pc, i also add a little reverb through the pedal itself to give a feeling of depth and space to each track. with guitars i record 2 tracks simultaneously and pan them hard left then do the same for the right, for the bass i do 2 tracks at once and have each one ever so slightly to the left and right of center, when programming drums i pann these as they would be on a real kit as if i where sat with the drummer facing me, IV found that panning like this leaves 'gaps' in the sound that things like vocals , solo's, keys ect fit into nicely i generaly try not to have to many things happening at once in the same panning channel as this leads to things getting a bit messy. theres not realy any set rules about it though its all reay down to personal taste.