If you're new to Deus Ex: Human Revolution, try playing the game on easyest difficulty. Make sure you check gameplay options in game menu, to enable item highlight, crosshair and more useful things. Save often and in multiple save files. Also a fiew other tips:
1). Try to use non-lethal takedowns as they make almost no noise, and reward you with more XP than lethal takedowns;
2). Stay in cover when moving around the area with enemys. Use objects in world (boxes, crates) by throwing them and luring out alone enemy for takedown.
3). Hide bodys after you took them down. Try areas that enemy rarely visit, vents, toilet rooms or just hide them from view.
4). Stay away from enemy cameras, turrets, robobots. Or look for ways to disable them, via the computer terminals.
5). Weapon with silencer is almost silent. Make sure you modify your pistol or rifle with silencer. Or use other silent weapons, like tranquilizer rifles, stun guns, crossbows.
6). Explore. Move around the area, check every corner, every vent, corridor. Look under boxes and crates as it may reward you with bonuss XP and hidden items.
7). When you come across pocket secretaries, e-mails or e-books make sure you read them in your logs, sometimes they hold login names and passcodes.
8). Hack everything. Even if you have found the passcode. Successful hacking rewards XP, credits and hacking software (stop and nuke).
9). Make sure you do side missions (blue colored) before you advance with main mission. Check secondary goals for your missions, they often reward in various ways.
10). Spend your praxis points. Make sure you spend them on augmentations you realy need.
Fiew useful augments:
1). Hacking Capture - will make you gain access to any computer terminal, security grid or alarm panel. Level 5 is a must. To control turrets and robots you need to upgrade your skill further, and it's worth it.
2). Hacking Stealth - is also very useful, as it will make you less detectable while hacking.
3). C.A.S.I.E. - is social augmentation that can help you convince NPCs to open up and give you more information via cutscene dialogue.
4). Punch Through Wall - often hidden secret areas and passages are covered by weak walls, you can punch through these. These walls will highlight.
5). Carrying Capacity - adds more space in your inventory.
6). Move/Throw Heavy Objects - you are able to lift heavy objects in game, you never know what's behind a fridge or crate placed in front of vent.
7). Icarus Landing System, will make landing safe from any altitude.
8). Energy Level and Recharge Rate - both useful. Will make you hold more energy charges and increase the recharge speed of your first cell.
9). Multiple Take-Down - you can takedown two enemys at once with cost of one energy cell. Useful when you see grouped up opponents.
10). Jump Enhancement - lets you jump higher. Very useful to reach secret areas.
Well these were fiew useful augmentations. There are more ofcourse. Some make you invisible for short time, some protect from damage, EMP-electricity, gases, concussion effects. Others let you see through walls, run silently and more. Make sure you read through descriptions, but remember it's hard to get every augmentation as praxis points are hard to get.
Good luck and have fun. Ancron (steam)