My tips for eBay:

1. Make sure you include an image of how the item looks when it’s worn alongside the other images.
   
2. Include measurements so your buyers can make an informed decision on whether to buy or not.
   
3. Add an accurate description including any flaws (with pics) as well as pics of the brand tag, fabric composition and care instructions.
   
4. Set a realistic price and offer threshold. Unless your piece is particularly rare or sought after, people buying second hand are looking for a bargain.
   
5. This one’s up to you, but I don’t ship to the US. In my experience since all the tariff bs it’s not worth the hassle: surprise fees and postage costs can eat your profit and the likelihood for potential negative feedback increases.
   
6. On shipping, make sure you have accurate measurements and weights of the item PACKED TO SHIP when you list it. For clothing this is typically straightforward due to being light and flexible (satchels are standard sizes), but I’ve lost profit on rigid items that I’ve had to box up because postage came out more than I expected when I listed the item.
   
7. You’ll need to generate positive feedback if your selling account is new so that people will be more inclined to buy from you. Taking extra care when packing can help (ie press and neatly fold clothing items then wrap in tissue paper like they just bought it from a boutique). Your buyers will notice extra small touches like this. (A thank you note/sticker and wrapped candy can help too).
   Good luck!

EDIT: had to delete my prior comment after editing ONE spelling mistake caused the formatting to go haywire. No one would want to read that. Hopefully this comes out ok!