tigertea, some tips:
Make sure you include the brand in the title and in the drop down that allows you to select the brand.
Do the same for the size, as many people filter by size.
I find that colourful clothes/bright prints sell much better than light coloured clothes, which tend to languish however good the condition or brand.
I rarely bother to sell any clothes that are unbranded eg GAP, Boden, Vertbaudet, OshKosh, Timberland, Next ... John Lewis will not attract much interest as a brand. I don't list unbranded items unless there is something particularly unique and attractive about them.
Sell summer clothes in April/May and winter clothes in September. I don't bother selling clothes outside these 2 periods.
End listings in the evening. For other items, I would recommend a weekend, but for children's clothes, you can end on a weekday because a lot of bidders are busy mothers who are about during the week after their children have gone to bed. Avoids the overcrowded weekends.
List all your clothes to end around the same time, rather than in batches over a few weeks. Cross-refer your listings eg in your Gap listing, say 'check out my other items in the same size, including Boden ...' - this increases the overall traffic.
Offer postage discounts.
Pay for a gallery picture.
At the end of the day, it must be a desirable item ie something at least you will want to buy yourself. I find this test to be quite accurate. No amount of tips can get past this one.
And, of course, luck!