Based on the principle that all post processing manipulation is destructive (you can only take data away, never create new data) the perfect would require no post processing manipulation except sharpening. But seldom is a shot/scan that perfect!
The secret is to do as little as possible, and to develop a systematic workflow, so that you don't end up contradicting one adjustment with a subsequent adjustment.
I work as follows
1 - crop/rotate as necessary - cropping is more an artistic than technical adjustment - what looks right? Though clearly the more the subject fills the frame of the original, the higher the quality (less grain/noise).
I crop width to 1024, but let the height vary to suit the shot. Personally I don't see the point of including more ground/sky just to bring the pixel height up to 768 - I'm usually happier with a long thin image.
2 - remove any dust scratches using the clone tool
3 - adjust levels and curves to get the blacks/whites properly set and adjust the gamma. I now like to adjust colour using curves, but otherwise...
4 - adjust the colour balance using colour balance, or in PS, the "variations" option is very useful since it gives you a mosaic showing the effects of various changes. Note that if you correctly set the black and white points in step 3, colour correction should really only need to be applied to the midtones.
In steps 3 and 4, we're talking fairly minor adjustments - gross adjustments will often create an artificial look and/or poor transitions betewwn tones - if you find major adjustments are necessary, you might be better to rescan if possible.
5 - Sharpen using unsharpmask (or one of the variations on the theme available as plugins for PS)
Colin K. Work, Pixstel