Overall there's not a lot of difference painting hands to painting other areas of skin in terms of technique or method, they're just a little more intricate so more akin to painting a face than painting an arm. The main thing that can tend to differentiate them in terms of colour is that the hand in general, particularly knuckles and fingers, can be a little redder than the skin elsewhere (unless the arm is raised). I often don't mix colours specifically for this, just rely on a little glazing to redden up those areas, with a few touchups on the highlights afterwards.
Most times we don't see the palms/inner surfaces done lighter in colour, but for any subject with much colouration to their skin that would be worth including if the position or shape of the miniature's hands allows.
The two most challenging aspects about painting hands in detail are probably the fingernails and veins, if you want to include them. The main difficulty with nails is their very small size in miniature and I don't think there's any substitute for good vision, steady hands, a sharp brush and practice (the way some fingers are sculpted or come out of the mould often doesn't help here).
Veins seem to be difficult because of their colour (which is undeniably tricky to pin down) but also the pattern/direction on the back of the hand can be confusing so it's often simplified or stylised. Luckily most of us have good references for this available any time we need them.
Einion
