Rest enough: : You might have 500 Ordella powder but with strangers you never have a clear idea on their habits and thinking logic. You are suggested to store a lot of mana instead of getting into trouble later. (in short, stock up, grouping with randoms means spending more resources.)
Be respectful and logical; some people will behave in a different way grouping with people they don't know. People will treat you in the same way you treat them. Be nice to people. It's a general rule that doesn't always apply, because there are always rotten apples in this game that don't behave in a respectful way.
Clear the loot rules before you begin, ask if people need certain items for which you may pass.