To create a great auction ad you need don't need to be a computer wize.
You need to describe your item - any marks, stains, holes, rips or anything you think a buyer will notice, i always approach my description like i am the buyer, to help me describe it best.
If you are selling anything that needs measures always add them to your item's description in centrimetres so your buyers can use a tape measure to get a visual of the size if they like, this is very important when selling shoes.
If you are using backgrounds, keep it simple, don't have to many moving HTML's as this will slow down the loading time of your auction page and some buyers will loose interest before even seeing your items. Pictures should be resized when using HTML to add extra pictures to a smaller size, again to save on download times and also so the buyer doesn't have to use the scroll bar to see your complete picture.
Make sure if you are using a background that your text is readable, a good sized font to make it easy to read, a good colour that doesn't blend into your background, where possible use a white background for your text to help your potential buyers read and understand your items description easier.
If adding a postage qoute/chart to your auctions, make postage clear if it differs between states/countries, clearly state if you require other additional things with your postage ie insurance/registration.
Clearly state your payment options and if you offer pick up to local buyers as this can be a great way to increase bids on larger items that you can not post.
If you plan to deliver an item to your buyer, make terms of delivery fees clear on your auction, so the buyer know up front there will be extra charges involved.
If you have special mailing days, it is good to list them to make your buyers aware that you don't post everyday.
The best advice is good communication is the best key to a good ebay experience for all concerned from start to finish with all ebay transactions whether you are buyer or seller.