Im about to write a pretty lengthy conversation in my novel with a character explaining and briefing the other characters about an expedition, any tips on how to keep it from getting too lengthy or boring?

You braid your narrative.

So, there are four types of narration:

Action: John moved across the room and kicked Larry in the head.

Dialogue: John said to Mary, “I think Larry is out cold.”

Description: Larry’s body fell limp on the ground, his face swollen.

Internalization: Mary thought, John is such an ass.

You’re writing a lengthy dialogue and, what’s worst, it is an exposition. Not only is lengthy dialogue boring, but exposition makes it worse. So you want to braid your narrative, braid all 4 types of narration into your exposition. So this scene isn’t just one person giving a lecture about what the team needs to do next, but you need to braid in some action: maybe one of the characters is late. Why is he late? How do other people react to him being late? Maybe your POV character has other ideas about how the team should proceed; add some internalization to your character and have him thinking about his previous expedition and why he didn’t think the plan would work. Add some description: where is your team? What did the environment look like? What does each team member look like, and how do they behave? And alternating all 4 types of narration through your exposition. So your exposition isn’t just one gigantic info dump, but it also pushes the plot, builds your characters, and builds drama and conflict.

Hope this helps.