I only list items I'm fairly sure will sell for a decent price.
I mainly do kids' clothes, and try to sell in season. GAP, Next, Monsoon and Boden all sell well as individual items.
If I have larger quantities of stuff from lesser brands (H&M, George etc) I sell it as bundles, which also works well, as long as you calculate the postage properly. In general, I aim to keep the postage costs reasonably low, but high enough to cover the cost of packaging and my time as well as the face value of the postal charges.
Wrt fees, I start the item at the lowest price it's worth my while selling for. I always put in a gallery picture, but never pay for any other fancy features. If I'm selling bundles, I do one photo for all the tops, one for the trousers etc as well as one photo of all the items together, which helps keep the costs down.
I have a spreadsheet in Excel where I enter the actual postage costs and the fees and deduct them from the sale price and postage I charged to work out the net profit per item. That way you soon start to see where you're undercharging and/or which items are not viable for sale.
hth