Very very nice pictures are essential, I have a feeling you can get up to 12 pix for free. Otherwise set your ad up, schedule it for 3 weeks hence & keep an eye out on the threads here for the first free-listing weekend (that way you can set your mininum price for free). Keep rescheduling if you miss the free-listing weekends until you get the right moment to send it live.
People disagree about best times & days to list an item, but 7-10pm is probably best. And not in the summer months, generally.
The best quality pix you can manage whilst sticking to true colours. Detail shots of any nice features on the item (eg, embroidery). Make the background as plain as possible (no clutter on view!).
I had a coat returned recently (grrrrr) as Item Not As Described. EEjit buyer. If I had to flog it again I would write "This is how the tag describes the material but I can't promise you'll think the same." statements. And don't try to describe condition, just say factual things along the lines of how much it's been worn, whether there are any repairs, rips or marks. Give explicit measurements where it's easy to measure, like waist circumference, inside leg, inside arm, collar to hem (inches & cm, ideally). Don't forget the brand, how long you've owned it, and what it's actually made of (silk or denim, etc.).
Don't forget to say "smoke-free", "pet-free", how it's been washed things, too.
Pictures of the item hung up & of the item lying flat can both be useful. See what other sellers have done & what you think looks appealing for similar items. Research similar items to see what they have sold for recently to figure out a realistic minimum/starting price.
Sorry I don't know a good way to do it all technically, I always find it quite a slog to get a nice ad together.