In no particular Order.
1) On screen arrow indicating where other is, maybe in the minimap too? (optional?)
2) pop up to player #2 when player #1 when they start talking to a npc that has meaningful dialog - with the option of warping/joining in
3) while you are waiting for the other player feedback on what they are in the process of doing.
4) option to AFK maybe just a little button like sneak that lets the other player know. But I had the crazy idea that they could also take control - so they don't have to wait for you to return. (I took a break then on returning had to ask, where are you now) alternatively, the ability to follow the other player.
(yes, I know, I'm lazy)
