Game play in a competitive match is faster paced and more intense than public games. Overall strategy is fairly similar, however much more precise.
A very generic match would start with aliens playing defensively trying to hold map control, whilst marines push through to cap res and destroy alien res (which is very important due to the alien resource system). The 2nd hive will be put up as soon as possible, and fades emerge at the same time to defend it, in this 3 minutes the main struggle for dominance occurs, and if the aliens manage to successfully complete the 2nd hive they can usually go on to win the game.
Aspects such as teamwork are essential in wars, players need to stick in groups and communicate effectively so they can cover as marines, or synchronize ambushes and assaults as aliens. Activity and frequent pracs (practise matches between clans) can then quickly lead to improvement, remember to reflect on any mistakes.
It may be worthwhile to check out some various guides available on the site. Watching demos of good teams can also be helpful, NSPlayer, AusNS, and Amped News all host demos for download. To watch a demo put the .dem file into your half-life\ns directory, start NS, bring up the console, and type "viewdemo filenamehere". Remember, demo's will only work if they are from the same version of NS, older games may not be viewable.
Thankyou for taking the time to read this guide, hopefully you should now know anything you need to get started and into the competitive Natural Selection scene. If you need further help or have any questions about NS feel free to ask in the #NSPlayer channel or email/pm N3 or haymo.