- RTFM. Very important.
- Learn the maps, or at least A map. NS maps are large and fairly complicated, so having some knowledge of where to go really makes a world of difference. Eclipse is a good starter map.
- Use voice comm. It makes team coordination much, much easier.
How to play as...
Marines Each marine is very versatile. You start off with a decent weapon and have the ability to construct any building the commander places. Travel in groups of at least 2 (preferably 3 or more), cover each other, don't bunch up, and check your six. Use your ears, since aliens have pretty loud footsteps. And don't forget to look up when entering a room, since those bastard Skulks like to hide above you.
Being a commander is a tough job. Keep him informed of your situation, but don't bitch him out if he's not doing what you think he should. Do what he tells you, since he has a much better view of the big picture.
Kharaa (Aliens) The Aliens' strength is that each class is very specialized in their strengths.
The spawn class, Skulk, is great at ambushes and raids.
The builder class, Gorge, is quite vulnerable to the enemy, but is critical to the success of the Aliens.
The flyer class, Lerk, is a skirmisher/combat support unit that can be a huge thorn in the enemy's side if played effectively.
The footman class, Fade, is the first unit that can effectively tank against the enemy, and the only class that has a powerful ranged attack.
And the assault class, Onos, is a elephant/rhino monster that can serve as a spectacular spearhead into an enemy base.
The true power of the Aliens lies in different people supporting each other with complimenting classes. Use your hivesight to see where trouble is, find a job and do it. Your team must be able to react instantly to threats and opportunities if you are to succeed.
Gameflow Info The aliens gain additional classes and abilities by securing Hive locations at certain points of the map. Alien success relies on them grabbing a second hive quickly. When they build the third and final hive, all alien powers are unlocked and the marines are at a great disadvantage.
The above knowledge should guide your strategies, no matter which side you're on! The marines must do everything in their power to prevent the aliens from controlling the third hive, and should mount an offensive on the second hive quickly. The aliens, conversely, should do everything in their power to grab a second hive, and should mount an offensive on the third hive location as soon as possible.
Marines "climb the tech tree" in typical RTS fashion, creating buildings and researching advanced technologies. This means that they are wholly reliant on resources in order to advance, and thus Marines should go to great lengths to protect their resource nodes. Aliens should go to great lengths to destroy them.
Those are the basics. Remember to do what's best for the team. If you're a new player, please listen to those who sound like they know what they're doing. NS has a bit of a learning curve, and it will take some time to become a competent player. Working together is the key to victory.