I played XCom most of the day yesterday, having been about 7 hours in at that point. I had gone through the long tutorial-ish part, and was well into the main game, at least 2 months in.
And I was seriously screwing things up on the Macro side. People have been praising XCom for it's elegant combination of the micro (combat) and the macro (running the base.) Yes, there is a balance between the two, but they actually do a poor job of teaching you how to run the base - even though they have this long, "training wheels" beginning to the game. They problem is that there are many elements to account for, and if you screw up on ONE element early, it can kill you.
And it was killing me. Shortly after I started playing yesterday 3 countries pulled out of Xcom, my finances were crippled, and I had no idea what to do. Why is that? The game didn't tell me how important Satellites were early. They were just one of many aspects floating around, but after my version of XCom started crumbling, I did a little research and learned just how important they were in the early game.
So, in summary, I wish I knew how important satellites were before I started playing XCom.
I realize this probably happens to a lot of us, so what's your "wish you knew?"