I've been in a few threesomes and one five way. The bad ones involved people I knew.
Ex. 1. I had a not very close friend who wanted to try a threesome. He had a friend who wanted to try one. So we did. Problem was, I had no interest in having sex with my friend, but his friend was sexy as hell, and the friend of my friend and I got it on while my friend tried to join in several times, unsuccessfully. So he got pissy with us (it was at his apartment) and left the bedroom. We finished up and both of us left. I got a room at a hotel room near the freeway and the friend's friend spent the night with me.
Ex. 2. A guy I met on Scruff and had hooked up two times messaged me to ask if I wanted to join him and another guy he had just met on Scruff. I looked at the other guy's profile and agreed. I didn't know either of them, except the two times I had oral sex with the one guy. Not knowing each other was sexy/mysterious, and I had a fun time. All three of us got off, mingled in the shower both before and after, and parted ways a couple hour later satisfied.
Ex. 3. A guy I briefly dated texted me with a threeway proposal. I told him I might be interested. A group text then started – we shared pics and went over expectations. We would show up freshly showered with meticulously clean assholes, in easy to remove clothes (athletic shorts, t-shirts, and flip-flops), I hate "gear" like jockstraps, cockrings, and anything leather, as well as strong colognes, so we agreed to leave those at home if you had them. The stranger said he loved to have his ass eaten but did not like giving head, and so on. It was almost clinical in preparation, but it was the best sexual experience I have had with more than two participants. We agreed in advance whether we would drink or get high (drinks ok, drugs not ok). I attribute the success of the experience to careful planning.
Ex. 4. A guy who lived in my apartment building knocked on my door one night and said a few of his friends were at his place and they wanted to get head. I'd never messed around with my neighbor, and had never met these friends of his. So I showered and went down to his apartment. They were sitting on the sofa and in two chairs, with their shorts off, jacking off. Straight (!) porn was playing on the TV. So I went straight to the nicest looking one and started blowing him. Pretty soon the others were telling me what to do and I was, mostly, happy to oblige. After having four of them in my mouth at different times, I wanted to find out what my neighbor was packing. But he wasn't interested; he just wanted to watch. An hour had passed and it became clear to me that they were not interested in ejaculating. It seemed like they just wanted to watch each other get sucked off, but not to completion. So I stood up and said that if nobody was interested in coming, I was leaving. And I did. I heard them later that night talking very loudly (the building's courtyard allowed noises to drift far). I didn't know what to make of the encounter, but it was singularly unsatisfying for me.
Good luck, OP. Try to plan in advance and keep your expectations low.