[HELP] what to do when trading for the first time?

I’m planning on buying The Sin: Vanish keyring version from Enhypen and if I end up getting a keyring I don’t want, I’ll be trading it (the other person will just have to pay shipping unless I decide not to). Usually I would get in contact with a friend who has done trades before, but she’s currently on break from trading or stopped altogether, so I’m pretty much doing the trading myself. Now, I have some idea on how to do trading, but I’ve mostly been the one receiving the item and considering I usually had a third person help with the trade (in my case my friend), I’m pretty much lost on what to do.

I’ll be doing the trade on Instagram as that’s where I’m most likely going to do the trading and it’s a platform I’m familiar with because I have participated in GOs on there before, but if I get no response, I’ll do it here on Reddit. I have another account that I’ll be doing the trading, as my main account is private and I don’t want to make that account public just for a trade. Any tips will be appreciated.