Cover, Cover, Cover
It may sound like a simple thing to say but make sure you’re making good use of the game’s cover system, if enemies find you out in the open they will make spare no time in plugging your full of lead.
Likewise, keep your head down. Line up shots prior to jumping out and firing and only emerge for a second or two at a time.
As an extra pointer, guns like the shotgun have some strange cooldown on returning to cover after firing, if you let go of the cover button you can walk back into cover quicker than Jensen will automatically return.
Bottleneck your foes
Unlike many first person shooters Deus Ex gives you the luxury of choosing the place to start most fights, letting you attract enemies by firing a shot. As such, choose your locations wisely.
Stay close to area entrances and try to give your foes as little room to manoeuvre as possible, this stops them flanking you, reduces their range of movement, and increases the effectiveness of blind fire should an enemy come running towards you.
Keep Your Distance
Close up, enemies in Deus Ex are devastating, but the further you get away the less effective they become. Unless they’re a sniper of course. If you can engage your enemies at range it gives you an advantage, Adam is able to take pot shots with a machine pistol or fire a 10mm at range with a surprising amount of accuracy.
Again, try to start a fight with distance in mind, rather than trying to create some range mid fight.
Iron Sight When Possible
Whilst shooting from cover feels accurate, and to be quite honest it is quite accurate, you’ll notice an even larger improvement using your guns iron sight whilst out of cover.
A good way to play this is to line up your shot in cover, then let go of the cover button and use the crouch toggle as your in and out of cover mechanic, using the iron sights to nail far away opponents with ease.
While the way enemies track your ‘last known location’ is more of a stealth thing, that doesn’t mean you can’t use it in a firefight. Get behind cover and move around, move away from hot spots and wait, enemies will become impatient before long and come to check if you’re still where you think they are, giving you great opportunities to land some hits on foes out of cover.
Dealing with Bots
Security robots are unarguably the toughest nuts you’ll face in the game if you’re unequipped to deal with them. An EMP grenade will dispatch a robot in one beautiful blue explosion, but you won’t always have one of them handy.
If you’re lacking in circuitry disrupting pineapples you’ll want to find a piece of cover you can freely move around in a circle, now pull out a heavy weapon such as a shotgun and keep moving around the cover relative to the direction the robot is moving, popping out to attack him with one or two shots and getting back in cover once its gun revs up.