The more you know about eBay the better you can focus your efforts on what will most likely improve your potential for success as a seller. Three distinctive and largely separate efforts are involved:
Getting your items found by shoppers
Getting your items visited
Getting your items purchased
Getting your items found
Getting one's items found by shoppers is, by far, the most challenging part of selling on the Internet. The greater potential for exposure eBay provides is the one and only reason many people sell on eBay. Even on eBay, knowing what one can do to maximize exposure is fundamental to success. Simply put, your job is figure out what paths most shoppers would probably use to get to the type of item you are selling. Then, do your best to make sure your item falls into those paths. Easier said than done, but just saying it gives some direction to your efforts:
Method 1: The path of least resistance
Consider that most shoppers will tend to take the easiest path. On eBay that translates to a greater liklihood for following links than for typing into search boxes. So, one approach you can use is to start at the eBay home page, eBay.com, and from there look for the (type of) item you are planning to sell by following the links eBay makes available to you. Each stop off along the way, on through to where you finally end up, are good candidates for the category to put the item into.
Method 2: Nothing succeeds like success
Try to find seemingly successful sellers of items similar to yours. Give particular attention to category chosen, construction of item title, and starting price as those are the primary search ingredients used by eBay and shoppers (that you have direct control over).
Do your own word searches and observe what the shopper is exposed to by eBay along the way. For example, eBay will often present alternate paths (categories) for finding certain items that you may not have thought of yourself. Just by experimenting and following hunches, you'll learn a lot. For example, I recently discovered that the category an item is put into amounts to the same as having put that category name in the item title. So, rather than using those same words in the item title it may be better to use others that could instead be used by shoppers to find that item.
Try not to waste any space available to you in the item title. Fill it up. Put in as many words as you can that could be used by shoppers if they do perform a word search for an item such as yours.
Getting your items visited
Bearing in mind that your item will be competing for the attention of shoppers in lists of search (or browse) results, what comes closest to advertising on eBay, short of paying for a featured item, is what you can do to distinguish your item from others in those lists. Most sellers ignore the potential of the gallery picture for that purpose yet, other than paying eBay for bold or other add-ons, that picture is the greatest opportunity you have for helping your item "stick out" in lists.
Crop the image you will be giving to eBay for use as your gallery picture to a perfect square before handing it over. It will then appear larger than most other gallery pictures. In the process consider cropping down to only a portion of the item that would tend to attract the most interest.
Consider adding a colored border around it. With EAPH hosting a fuzzy border of any color can be added to a photo using the Optimize tools.
For high end items consider adding text to it.
Getting your items purchased
Once you have a shopper looking at your listing, believe it or not, your job becomes relatively simple. The advertising phase is over because you've already attracted their attention - no need for bells and whistles. All that's left, basically, is to to is give 'em what they came for. That will vary depending on what you are selling but here are some guidelines that are almost universally applicable...
Be generous with photos
For most items showing good photos is the first priority because no matter what else you do, shoppers are not going to bid or purchase unless they like what they see of the item. Show as many photos as it takes to eliminate any possibility that the shopper might want to see more of the item before making the decision. When choosing or building a template consider as a primary goal that it accentuate the appearance of your photos.
Take as much space as you need
Resist any thought of needing to be brief merely for the sake of providing a quick in and out for window shoppers or from the belief that a concise item description is "more professional". A buyer wants and expects you to provide a thorough and accurate representation of the item using photos and textual description. How long your item description becomes as a result of fulfilling that obligation is simply how long it needs to be, period.
As you build your presentations imagine you are speaking to buyers who are truly and genuinely interested in what you are selling. That will help you have a positive attitude which will, in turn, be reflected in your presentations. Consider what buyers will want to know or see. What questions might they have. What might they want to know about you that isn't covered simply by feedback ratings. In short, don't be shy or modest in the sense that you leave out information that could be helpful in swaying a shopper toward the decision to bid or buy.
Favor content over style
A well organized attractive item description adds value to your item for sale and helps portray you as a competent and reliabile seller. Achieving that requires the structure provided by use of templates such as you can create for yourself using FreeForm or by purchasing from a designer. When choosing or building a template consider that a relatively simple layout will be much easier to work with and provide more flexibility in display of photos and text. In the overall scheme of things those practical considerations will serve you (and your buyers) better than a template layout that requires content to be squeezed into specific locations in specific sizes.