when i play a "premade" its usually only 1 other guy i know.  So that means we still have 1-2 random players on our team.  More often than not these "pick up players" will in fact work together with us and or suggest things to do.  I work with random players all the time coordinateing upgrades and locks.  Also I'm always communicating in chat, not via voice.

--shopping

--getting gold 1

--Can someone get tower regen 1?

--2 demis incoming "xplayer"

--whoops sorry i overextended and died

I find for the most part this works just fine and besides the occasional jerk most people try to work with you, offer up suggestions for things they want to do, or back you up.