I have only sold one thing and it was a TV I won and it was local pick up and was 60% cheaper than what was in stores so I made money either way.
My advise would be sell products that are value for money, good priced postage(none of this add postage in price and then list free postage), use a good delivery method(i have seen many sellers get neg feedback because of a slow delivery time(even if they cant control it)), best thing to do is to have the product boxed and make sure the item is protected, then write the address on the label and sent as soon as payment is made.
A good selling page with correct information, you can do this by going to the product site(eg samsung.com for a PC monitor with all info, specs and some reviews or feedback for that item listed in the description page).
Best way to make a description page is by HTML, use programs like frontpage to help you code it or a text editor like context.