I don't know if there is a thread like this but I decided to write down some basics non-systematically, in the order I recall them. This thread actually inspired the idea although I gave some tips to some beginners in the game I didn't think of a thread.
This is a great game even though there are bugs, cheaters, poor support etc. It may take time getting used to it but patience will be worth the fun you'll have. Even the cheaters won't be that much frustrating once you get used to Crysis 2 because you'll not be beaten by most of them all the time.
There are a lot of things to be said, discussed but let's come to the point...
1. Make friends; there are a lot of good people here. This is the real fun, playing with friends.
2. Your FPS is important. If it drops under 30 frames per second, you may think of yourself a bad player which is probably not true.
3. This is Crysis 2 and you have a nano suit which doesn't make you superman but superior than man. So forget about every experience you've gained from other FPS games.
4. Be patient while improving your skills, in action, in shooting, in defending etc. Do not rush.
5. Every nanosuit module, weapon, weapon attachment have their own advantages and disadvantages. You have to find good combinations of them according to your style, which game type you play and how you play.
6. You have a nanosuit which makes all the difference and it needs energy. Use your nanosuit and energy wisely because that's the key to survive.
7. At first your armor is weak and you get killed quickly. Improve it.
8. Always engage armor by pressing that Q key before you shoot. Make it a reflex. Never shoot while you're cloaked because that runs nanosuit energy off.
9. Change some keys if you are not comfortable with the default keyboard settings.
10. Do not be a camper. Because someone will find and kill you soon if you camp somewhere.
11. Always have an eye on radar and be aware of your surrounding.
12. If you are out of energy hide and wait then do what you wish. Do not hurry.
13. Try to flank the opponent. If you are flanked and someone is shooting at you, quickly change your place, jump in order to avoid more damage at the moment while turning to enemy and fire.
14. Alway be on the move.
15. Move left and right while shooting do not go forward. This makes you more accurate and harder to be killed.
16. Use nano vision if you are suspicious that someone is close or onto you.
17. Laser sight makes rifles less recoil. That's why lots of players use it while more exposing themselves.
18. If you are cloaked, you die quicker. Stealth makes you more hidden but more or even most vulnerable to enemy attacks.
19. You can destroy ceph gunships with 3 rounds of M2014 gauss and 4 rounds of gauss attachment fire.
20. Run in zigzags, not directly like trying to make a perfect line.
21. If you've killed an opponent and half the magazine is left, do not immediately reload. Wait sometime and check your environment. Because his teammates seeing the action on radar may be onto you. Do not rush to collect dog tags for the same reason.
22. Suppressed weapons' fire is not shown on radar.
23. If you are short or out of ammo while shooting at an opponent, do not reload. Switch quickly to your pistol.
24. If the opponents are far away from your firing range, take your time and tag them.
25. Level up your nanosuit modules since every level gives unique benefits of its own.
26 Do not give up. Be strong, be fast, be invisible, be the weapon.
I guess these are the most basics as I recall at the moment. If you've read these you are already a better player.
Additions and other tips are appreciated.