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!
TRY AND KEEP EVERYONE ALIVE
This can't be emphasised enough. As your troops kill aliens and complete missions, they'll level up in rank, unlocking new abilities and perks that become essential later in the game to bringing down more difficult opponents. Let too many of your best men and women die and you'll be stuck with a bunch of rookies, and you don't want that when the really tough guys show up.
You don't need to frantically save your game every turn and keep everyone alive, but you should aim to have at least 10-12 experienced soldiers on-hand at all times.
CAMPING FOR VICTORY
Take extra special care of your snipers, because the abilities they unlock can alter the shape of an entire battle. An experienced sniper with a good rifle and elevated vantage point will dominate, to the extent they'll easily rack up twice the number of kills compared to your more intimate troops. There's even an ability where they can take two shots per turn (everyone else only gets one), and those shots are usually insta-kills. Handy, that.
So always take a sniper. And make sure it's a good one.
Support classes, with their high range of motion and (eventual) ability to carry more than one medikit, are crucial. Especially for some of the longer story missions. You'll frequently need to regroup and heal your soldiers, and you don't want to be sweating your health as you draw in to the final few encounters. Bring a medic, or better, bring two.
THAT'S WHAT FRIENDS ARE FOR
After playing through part of a campaign on preview code with the default randomly generated names, I (Kirk) started naming my characters after friends and co-workers, and even customizing them to look a bit like my friends. That has caused me to become hugely attached to my characters, but in a good way—even if they die in combat, their sacrifice is always noble and heroic, and I do love to tell the actual people all about their exploits in my game afterwards. (The world will remember Luke and Owen for their selfless deeds.) Twitter can be great fun for this—I suspect that over the coming weeks, more and more people will be hearing of their last-second grenade tosses and snap-shot pistol rescues in 140 characters or less.
Unless you're racing to finish the story, you'll continually have options as to what to focus your research on. Luke's recommendation: focus on armour and plasma weapons. If you're not rocking Titan Armour and plasma rifles by 2/3 of the way through the game, you'd better have a whole bunch of coffins standing by at XCOM HQ. Indeed, it's not even worth bridging your ballistic weapons with laser gear. Just shoot straight for the more powerful plasma. (Damn, I wish I'd read this one before I spent so much time researching laser weapons. -K)
SAVE OFTEN, BUT NOT TOO OFTEN
It is possible to obsessively save your way through missions, perfecting your strategy and working every encounter to your advantage. And while of course, you should play with whatever style works for you, as you get better at the game, it can be enjoyable to dial back the number if mid-mission saves you allow yourself, and to live with the consequences of your bad decisions a little bit. And remember: It doesn't appear to be possible to game the system by reloading just before a shot until the percentages work out in your favor. Once the game has decided you'll miss a shot, you'll always miss it. Of course, I (Kirk) have only heard that and have never tried it because I WOULD NEVER DO SOMETHING LIKE THAT.
You'll quickly have the space to take six soldiers on a single mission, leaving you with the question: which soldiers to take? While some situations call for certain combinations, for most battles - those taking place outdoors and asking you to do nothing but kill a bunch of aliens - your best bet is one sniper, two support (both packing med kits), two assault and a heavy. The sniper observes and supports, the assaults kick the doors down and do the dirty work, the supports stay behind for mop-up shots and healing and the heavy...can do whatever they want. Which is usually putting a rocket in the middle of a room full of aliens.
DON'T HOARD YOUR POWERS
When you're in combat, don't hoard your abilities, ammo, explosives, or special moves. Use them early and often. Especially on the standard abduction, terror and UFO crash missions; most of them involve only 8-12 enemies, and you'll almost always end up with a bunch of leftover grenades, rockets and medkits. They'll save your ass more than once. Longer story missions are the only times when you'll want to think about pacing yourself, and even then, a live heavy with no rockets is much more useful than a dead heavy with two.
The simplest and most effective tip for battles is to use the "Overwatch" ability. Every. Single. Turn. Unless it's a timed mission (of which there are a few), you can afford to move at a snail's pace, because the defence and covering firepower you get from the ability is the most effective way to keep your squad safe. And remember, you really, really need to keep your soldiers safe! (Yes. This. Overwatch is key. -K)
THE MEN WHO STARE AT GOATS
When you first encounter psi training, it would be easy to write it off as a gamble, or a highly-specialised ability that's rarely used. Nope. While more complicated abilities are a little hit and miss, the basic psi attack does nothing but cause damage, and does so with 100% accuracy. This makes it the perfect clean-up weapon for those enemies who are stuck with half their HP left but who are in a position to hurt your troops.
PLAN YOUR FLOORPLAN
While some aspects of the base management are a bit bare-bones, your base's layout can still be easily maximized to your advantage. Leave room to build at least two of everything—laboratory, workshop, power generator, satellite uplink—and remember that vertical and horizontal adjacency give a bonus. Don't dig deeper than you have to at first—use all of your lateral space before spending money expanding downwards. Try to keep ahead of the curve by building labs and workshops before their respective delegates start nagging you to expand.
HOW TO MAKE FRIENDS AND INFLUENCE PEOPLE
You'll lose soldiers in this game, and you'll probably lose council members, too. Don't sweat this. You can afford to lose a lot of them before it's game over, so just focus on keeping the wealthy ones (each nation pays you a different monthly amount, so make note of this) happy. You'll survive if Nigeria pulls out, but if the USA leaves XCOM, you have problems.
DON'T FORGET THE LONG GAME
Related to that last tip, don't forget the long game. It's easy to put all of your money into developing sweet kit for your commando squad, but it's all for naught if your coalition falls apart. Remember to build and deploy satellites, planes, and other resources around the world, and when you're given the option between three abduction sites, pick the one with the highest panic rating, unless they're all high, then pick the wealthiest country. But remember: It sucks to make it 25 hours into the game only to realize that while your squad is nearly unstoppable, you're woefully underprepared to fight the long war necessary to win the game.
RUN FOR YOUR LIFE
Remember, this is a turn-based strategy game in which most missions are without time limits! So when you find yourself in a tight spot, or up against one of the super-tough bad guys near the end of the game, don't be afraid to cut and run. Moving around corners will generally get you out of their sights, and a full-blown retreat can be useful either to get enough space to heal wounded soldiers or, even better, to lure aggressive enemies into a trap. Preferably one full of snipers and heavies with rocket launchers.