part of the answer depends on the item. for something that is say a pair of earings for $2 you dont have to say. "blue earrings" can be your entire description and it will sell.
that said you want all the basics:
size (measurements not small/large)
color
material
as you ask for more money you want more info.
why is it worth what you charge
why is your product better
how does your product improve the buyers life
i dont think my descriptions are perfect but they get the point across.
you see too that i focus a lot on why it worth what i charge:
http://www.etsy.com/listing/76472472/40in-x-40in-baby-blanket-pure-alpaca-where though, i focus instead on how my product will benefit the buyer.
http://www.etsy.com/listing/80352999/merino-wool-scarf-mens-womens-luxuryin this case the item is less expensive and the buyer (i am guessing) is more interested in the style and materials than about the labor hours or other crap.