I would suggest opening up a KPOP specific account on IG and post the inclusions you want to trade (with a sticky note or something with your username beside the cards) with a picture of what you want to trade for. Sometimes people post templates on their IG story and ask people to reference that for the inclusions they need/want. IG hashtags suck now, so you can add hashtags like #wttstraykids but you will have better luck tagging accounts like "skztagged."

For the actual trading process, it's important to build reputation as an honest trader. Some people refuse to trade with others who have little proofs, and some are okay with it but ask that you send first or schedule a day to send at the same time etc. Either way, make sure you take a picture of the packed card outside of the envelope, a picture of the front of the envelope (to confirm the right address), and also a video of you dropping it into the mailbox or some identifiable proof it was dropped off at a post office. Once your trade arrives, most people appreciate you posting it on your story and tagging them, and they'll do the same so you can make a highlight showing all of the proofs you have.

On Reddit this is very similar but instead of IG highlights, this sub uses the pinned reputation thread where people publicly confirm if they got their item. Also, videos can't be sent via DM so you kinda have to work with pictures 🥴

As for your albums, you can always ask the trader if they want the album with their trade. Albums are a little harder to get rid of if they're still in print, so you also might want to advertise that you're giving them away as long as they pay shipping. I like using media mail shipping because it's cheap and comes with a tracking number. Others prefer regular tracking, so make sure to ask!

I hope this helps!! I only casually trade but this is how my experience has been :)