I have failed to save the Earth many, many times. More elite soldiers under my command have been summarily shot in the face by 3ft tall aliens than I can remember. Since we received early access to XCOM: Enemy Unknown I've played almost thirty hours of the game in Ironman mode, where every choice, mission and death is permanent. I've not saved the world, but I've learned a few things.
This video guide is intended to help you skip a few of my mistakes. I cover what to buy, who to send on missions, what to research and what base upgrades and mission rewards to pursue. It won't save you from watching your most beloved veterans die, but it'll hopefully prolong their lives just a little.