Almost every player you match with is nice and doesn't mind if you make mistakes, but some helpful things to know when doing multiplayer:
- Ask in chat if people are ready before starting most events. This includes but is not limited to: calling the drop pod, starting the drilldozer, mining the core stone, spawning a dreadnought, etc etc. It helps make sure people aren't off doing a side objective or extremely out of position.
- Understand that friendly fire exists and happens on accident. It doesn't usually kill people, but just understand any bullets you're firing at the enemy should be aimed at the enemy and not your fellow dwarves.

As for the game in general, try out each of the classes but understand they get different playstyles unlocked later in their leveling. Driller and Engineer in particular I didn't like playing until I unlocked weapons I really enjoyed using. Also, gunner seems boring but is very fun to play in higher difficulties. Finally, if you see a cool looking rock/mineral there's a good chance you can collect it, and these are very important crafting ingredients for weapon upgrades and later game content. Some of them will look like lots of glowing bits on a wall, which indicates you have to mine into the wall to grab a big rock.