One rule before any other.
Do not clean a coin
Ever. Not with polish, not with lemon, not with a cloth.
Collectors price the original surface, and cleaning destroys it permanently. A dull, original coin is worth more than a bright, cleaned one — frequently several times more. The marks that cleaning leaves are visible to anybody who knows the series and they cannot be undone.
The same goes for notes: do not press, flatten or repair them.
What decides the price
Rarity within the series — the year, the mint mark, the variety. Age alone decides very little.
Strike quality — how well the design transferred.
Surface and lustre — original, or disturbed.
Grade, where it has been assessed.
What to show
Both faces, held still, with the light moving rather than the coin. Lustre only reveals itself when the light moves across it, and that is something a photograph genuinely cannot do.
Then the edge — reeding, lettering, or plain. Frequently the most informative part and almost never photographed.
On attribution
Say what you know and how you know it. "Catalogued as X by the previous owner" and "I have attributed this myself" are different claims and buyers treat them differently.
If you are unsure of a variety, say so and let the room tell you. Collectors enjoy that and will often tell you something useful.
Delivery
Small, valuable, and the one category where a lost parcel is a serious claim. Packing coins.
More: how to sell on Metzee, pricing coins.