I will give you a simple steps, I hope it will help you:
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Find a really nice clan name, that interest and surprise the player.
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You must be active at least 4-5 hours, to let the players know that you have a clan.
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You must be a professional player.
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You must have a nice server.
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Create a nice Forum/Website.
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Offer players to join your clan.
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Be friendly with your teamate, and with players.
That's it, as simple as that.