Reply #2: It's been a while, but

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Check that the servers are clean, i.e. no aimbots / 'see through wall' hacks etc (reputable servers only). Increase your mouse sensitivity, it'll take a while getting used to it at first, but it really helps. Do you 'strafe' effectively? If not, I recommend you learn how to keep your sights on the opponent (play in bot/single player mode for practice) while evading their fire. And lastly, stealth pays off in a big way on some maps