I was a former bouncer at a shitshow nightclub for more years than I care to admit. The only reason I stuck around was the girls, free alcohol, and generally just being young and dumb.
My general recommendation. Muay Thai, basic wrestling and BJJ to stay off the ground. Learn to get up from the ground.
I am naturally a tall, explosive, fast twitch guy, but when I started I had no experience in ugly fights like that. I didn't know shit. And we were literally fighting every weekend for years, sometimes twice in one night. I had to learn fast.
I learned from a coworker, a mma fighter/bouncer to stay off the god damn ground. Trained with him often.
Basically, don't get into a tussle or clinch, pull guard unless absolutely necessary, stay mobile, light and fast.
Every 1v3 usually starts 1v1. Think about that, you're in ground working that pretty triangle choke and suddenly his buddy comes out the club and stomps your skull.
We mostly fought inside or just outside. We rarely got involved in fights beyond a certain distance at our club in the street, but we could watch. Bjj and wrestling are great bases. Its great to know how to clinch, I used it when forced to. But I witnessed dudes lose to bar brawlers far more often than win at the exact moment they restricted their ability to retreat. They usually start off winning, but theres just so many unknowns on the street and sometimes it's ok to retreat. You cannot run from your backside and I saw alot of people lose that way, or even in a clinch situation.
My strategy? I have a 81" reach. I switched my power hand to the front and used it as a jab/counter punch. I faked it as a typical slow unthreatening"stab" jab, but when they got in range I unloaded full force. I worked it circling away from their typical haymaker. I practiced Muay Thai style round and front kicks every other day for years. Very low trajectory, knees, pelvic, balls. Well over 150 fights, some were 2v1 and I never lost. I got clipped, sucker punched, scratched, slapped, spit on, hit with a flying pool stick, pool balls, beer bottles. Lol.
Find out were your strengths are, but stay on your feet! Can't stress that enough. Even days when I did not work we would watch the camera and it was some poor soul getting jumped after it was 1v1 and he was on the ground, usually winning until homeboys showed up.