I'm a big believer in getting rid of or selling what I don't use on a regular basis (and now that we're downsizing, I will definitely be listing a ton of things on eBay).  I specialize in selling clothes, and especially bags.  Overall this tactic has worked out really well for me, and I've only regretted selling something a couple of times over my 10 year experience of selling on eBay.  Yes, a decade!  Even I can't believe it.  

And in those 10 years of selling I've learned a thing or two and I'll share them with you here:

1) Take really good pictures.  It makes a huge difference when you can take pictures that appeals to a seller and it will make your item sell twice as fast.  About 7 years ago when I moved to SF, I purchased a dress form (like a mannequin) from a business that specialized in selling old and used mannequins.  It was one of the best purchases I've ever made for my eBay business.  Clothes just look better when its on a mannequin.  I'm not sure if that business still exists but if you're serious about selling, I would recommend getting one {or if you're my friend, you're always welcome to use mine.}  

2) Along with a mannequin, good lighting is another must-have for good pictures.  I started with just one light/umbrella contraption and now I have 3, for max bright lighting.  This way I can take pictures even at night.  I got a light stand pretty much like this one.

3) Write concise but detailed descriptions.  First, list measurements.  For clothes I usually do from top to bottom (i.e. shoulder to bottom hem, or waist to bottom hem), and across (the chest or waist) when laid flat.  For bags do length, width, height and strap drop.  

4) I also list any defects that the item might have.  It's better to be upfront with it, not only because you have integrity as a seller, but also eBay allows buyers to force a return if the item is not as described.  And eBay almost always takes the buyers side.  Even though buyers can force a return, I don't usually allow returns since it's always a bit of a hassle (I write as part of my listing "No returns unless the item is significantly different from description").  If the buyer really wants to return it they always can.  

5) I also add in the description whether or not the item has smells (most of mine don't but I've definitely been on the receiving end of an overly perfumed bag and hated it).  I also say it comes from a smoke-free home (and if you don't have pets, I would add pet-free home too).  I'll also add an estimation of how many times or for how many months an item has been used and whether or not there are any tears, holes, or major signs of wear.

6) Here are some tips for the actual listing: I usually do "Good 'til cancelled" so that eBay will automatically relist it when the listing ends (usually after 30 days).  As for shipping, I usually do a flat rate.  I've been doing this awhile so I can kind of guestimate what the shipping would be per item (of course I'm off but a $1 or so but it all evens out in the end).  But you can use USPS.com to calculate shipping.  For international shipping, I go with Global Shipping program which means you're responsible to ship it to somewhere in Kentucky (the address shows up when you print the labels with eBay) and eBay will ship it overseas.  I don't really touch any of the other boxes (so you can pretty much ignore them).

7) Always save your listing as templates.  That way you only have to change the title, pictures, parts of the description and the price.  Everything else pretty much stays the same so posting listings becomes a breeze.

And November and December are the best times of the year to sell items on eBay since everyone gets into the buying mood.  I hope you found this helpful and good luck selling your things!