On one particular occasion, I auctioned a dress for 99p and it sold for £10.50 (so I was pretty delighted); however, the buyer opted to pay for untracked postage rather than the more expensive recorded - and lo and behold the parcel somehow went missing. I kept a proof of postage and sent a scan of the receipt to the buyer, and also gave her other advice such as checking if her neighbours had received the parcel by accident, or asking at her local post office to see if they'd had any undelivered post under her name. Despite my attempts to help her, she left me negative feedback, which killed my perfect 100% feedback average, thus scaring away customers - which leads me to my first point...
1. ...Always offer a tracked postage option
This way, you're assured of your parcel's whereabouts, and your buyer can't blame you for a missing item. If you're unsure of costs, find yourself a good pair of scales and weigh your package in grams, then check the price on Royal Mail's price finder.
Free postage is an option that eBay tells you will 'attract buyers', but you might want to consider raising the price of your item so that you're not losing money.
2. Take as many photos as possible...
...Especially if there are defects; buyers need to know exactly what they're purchasing, so get a good camera, plain or pretty background and bright lighting and get snapping. For example, if you've got a jacket with a missing button, photograph the front, back, pockets, sleeves, and the area of the defect.
I once had a buyer who demanded a refund because a button was missing. I had no recollection of there being a defect (I'm very meticulous about the state of my clothes), but I didn't have a photograph of the specific area to back it up.
eBay lets you include up to twelve photos on any one item, so you've got plenty of opportunities to ensure your buyer fully comprehends the state of the clothing.
3. Don't use empty adjectives to describe items
Buyers can detect that you're full of s*** when you continuously use words like 'lovely' and 'gorgeous' in your item descriptions. They want hard facts: the brand, the cut, the material, the size, etc. Be as descriptive as possible, as if you're describing the item to someone who cannot see.
Other statements you could make are whether your clothing comes from a smoke or pet-free home, or how much wear the item has had.
4. Block buyers that lack certain requirements
To assure that you don't get caught in a bad deal, use eBay's buyer/bidder management service to block buyers that are: registered in countries that you don't post to, have a low feedback score, have unpaid item strikes or don't have a PayPal account.
By doing this you'll increase your chances of bids from genuine buyers, rather than those who have ulterior motives.
5. Make the most of your item's selling points
I've noticed that I receive more views on items that are from popular brands, particularly Topshop, items that are brand new with tags (BNWT) or brand new without tags (BNWOT) and items that are in smaller sizes (as these can be difficult to find on the high street).
Make the most of these points as, along with the photo, these are the things the buyer sees first. So a good example would be (edit accordingly): Topshop Dress Size 6 BNWT. Avoid using anything but the main elements of an item, as these elements are what a buyer is going to type into a search bar - get it right, and your listing should be near the top of the search page.