Ok sweet so from a high level, there's some key things to bear in mind:
Bass Guitar: Centre (depending on genre it can be nice to have gritty overdrive tone and DI tone tracks)
Rhythm Guitars: Ideally you want one track panned hard left and one panned hard right for all rhythm parts (you need two different takes, can't copy/paste, as it's the slight differences in timing and how you hit the notes that give you a nice stereo image - copy pasting will result in tracks sounding mono i.e. down the centre with no width). For meaty parts (you'll hear it at times in Metal - I know Machinehead does it often and sometimes bands like Periphery, you can quad track parts - here you'd have two on the left and two on the right of each rhythm part - this adds some meat but affects clarity a bit)
Leads: Solo's you'd want Centre, harmonies I would have a track panned hard left and a double panned hard right (again, two takes for width) and on other leads it's up to you if you want some leads centred or some doubled and hard panned)
These tend to be industry best practice.
Drums: These are a real doozy. You generally get audience perspective or drummer perspective - I personally prefer drummer perspective but there's arguments each way. for drummers perspective:
Kick and Snare: Always down the centre
Hi Hat: maybe around 45ish Left
Rack Tom 1: around 25-35 left
Rack Tom 2: 10-15 Right
Floor Tom 1: 30-45 Right (I'd say 30 if you have a second floor tom otherwise 45)
Left Crash: 45 left
Right Crash 45 right
Ride: 35 right
Overheads: You should either have a left track and a right track or a stereo track with panning in place - either is acceptable but in the case of a left and a right track, be sure to pan them (just as a side note, when mixing other people's recordings, this is usually how you'd work out whether they mic'ed for audience or drummer perspective)
For the drums, these are approximates as I would say there's no absolute - whatever sounds best is right and a mix might call for specific adjusted values for things to fit. Basically, picture yourself behind a drum kit with the snare and kick right in front of you while looking ahead - where do you picture each drum piece in relation to centre?
When programming drums, you would either be generating a track per component or the software will be spitting out a stereo drum track. If the former, be sure to pan the multitracks when mixing, if the latter, see if you can set the panning in the software before exporting a stereo drum image (though personally I'd recommend a track per piece)
Then for vocals, you want a lead track down the centre and thereafter the sky is the limit really - personally, I like having a Left double and a right double to have nice wide vocals (panning depends on the mix - if a dense mix I'd pan like 80% Left/Right to leave space for the guitars etc. that are 100% either side. Also, harmonies and accent tracks can go down the centre or with doubles you can pan them).
