Isn't that question a little too broad? The problem I see with Magic players is that they tend to almost always play on auto-pilot, thus, making tactical errors by not exploiting situations where they would benefit from.

But, if I had to generalize this, I'll say treat this as if it were a control deck. For example, you're playing Landstill: you have 2 lands, a BS, Standstill and FoW in hand, and tapped out. The opponent has a Nactl in play, and is attempting the cast a Goyf. Almost always, you will pitch the Standstill. Unless you're winning or trying to break the symmetry, card quality is almost always superior. The only time you ever want card advantage while behind is usually against Control and Midgame decks. But I'll also be honest here, this theory still needs to be tested.