Saving the world ain't easy. It takes strategy, preparation, determination and more than a little luck. So don't be thinking you can just fire up XCOM: Enemy Unknown and see alien corpses pile up at your feet. Go in with that attitude and the only corpses you'll see are those of your trusted and highly personalised XCOM soldiers.
Instead, you might want to think about adopting a few of the strategies that got us safely through the game last week. They may not be the best for you, but they worked for us, so they're at least worth considering!