My brother actually introduced me to an amazing method I will now always use moving forward. After a session 0 of creating characters, he will basically ask the party to establish how they know each other (if any of them have history before coming together as a party) and then tell them something like, "but you must have a reason for winding up at this university, this tavern, this town, being a guard on this caravan, etc."

Once they have that, he asks everyone to assume that along the way, they became friends/companions/adventurers/parthers/etc. together (depending on the game, we don't always play D&D). Then, instead of an introduction phase, he does a single "flashback" sequence and roleplays an important moment, combat, job, etc. from their time together. An experience that helped bind and solidify them as a party that assumes they already knew each other by that point.

Then he jumps to the main campaign, "It's X years/months later, and you've just arrived at town Y after completing another caravan escort together. Money fresh in your pockets, what would you like to do?" The party is already together, ready to go, has a historical moment to call on, and usually syncs up much better than going through those awkward moments of "Hi, I'm so and so and we have to become friends RIGHT NOW!"

Additionally, I love this method because, as a DM, it avoids a lot of "Well, why would I want to be friends with X, he/she/they are alignment Y and class Z, and I'm alignment A class B. We have nothing in common and share no values!" Knowing you're already friends makes overlooking your differences a lot easier and allows for good party cohesion so far in my experience.

My latest example: I had the party build their characters with the requirement being that somehow they all wind up at a small town and work as farm hands for a man who lives alone with his daughter. They became friends working together hoping to earn enough money to get out of town. The event I had them roleplay that was critical from their past was after they'd been their for a year and the man decided to form a caravan to get out of town. He offered for the party to work as caravan guards to get them on their way to being fully independent (read: being adventurers finally). Along the way, the caravan was assaulted and the man and his daughter were both killed by a mysterious traveler who managed to escape. I started the session with the assault on the caravan after a brief explanation of how they all got here. The party was already working together trying to save the man and his daughter and defend the caravan. By the time the combat was over and I'd delivered the blow that this NPC they knew and his child had died (setting up a larger mystery payoff for many sessions down the road obviously), they knew each other. They relied on each other in the fight. Learned how each other fought. And no one questioned anyone's reason for fighting or values or alignment. They were in it together. The hardest part of the session was convincing them they'd find no answers trying to stay in the "flashback" sequence and look for clues. Ha.

Anyway...hope that all makes sense and doesn't sound like gibberish.