Take multiple pictures, including front, back and close ups of the pattern or any quirky parts (strange cuffs, interesting buttons, split in skirt etc.)
I found much more success when I bought a mannequin like this Half torso Mannequin . It's really cheap but made a huge difference to sales. I don't like seeing pictures of the previous owner wearing the clothes, it made them seem more 'used'.
Write a good description, so instead of 'M&S white blouse - size 10' write more information along the lines of 'M&S white cotton blouse. Size 10, but would fit a small 12. Measures 17 inches from underarm to underarm, 25 inches from shoulder to hem. Only worn twice. Like new condition.'
Use common words in the description. Instead of writing 'Maroon' say 'red'. Instead of writing 'houndstooth' write 'checked' (or 'checked houndstooth'). People generally aren't very specific with their searches, so try to make sure your item appears on as many searches as possible.
Time your auctions to finish on Sunday evening. That way you get all the people who've had online shopping time over the weekend. People like to bid at the last minute, so if they have to remember to bid at 2.48pm on Wednesday they might forget.
That's what worked better for me, but ebay is unpredictable sometimes. Some items sold for peanuts, and others had bidding wars.
Good luck!