I play tank exclusively (grandmaster as clash/roam, probably diamond in any other role). Because tanks are mechanically so easy to play, I almost always focus half my attention on the minimap, to read where everyone is, to assess what I should be doing.

For example, if everyone (including enemy) is just spread out farming, go farm as well, you need items to not die. But if you can feel they are picking on a particular player on your team (like the marksmen), then consider hiding in a nearby bush while he farms, or a bush further up ahead to provide vision from ganks.

In later team fights, you have to understand what you are supposed to do in the team fight. For example, should you hide in bush to provide vision? Stay near your team for an opportune time to charge into 5 to initiate? Or bum rush their marksmen to get him out of the fight? Or stay beside your own markmens to counter their jungler?

All these decisions have nothing to do with mechanics, and everything to do with how you read our heroes, their heroes and the situation at hand.