Decide what type of clan you want. Do you want to create a clan to play weekend matches for fun, or you take gaming seriously. In the latter case, make a professional E-sports clan to participate in major tournaments and earn rewards.
You need to be a top player to attract decent players to your clan. So work on your game and keep playing till you are confident that you are recognized as a pretty decent player in the gaming community. As you improve your game, you will meet other good players in matches. Talk to them using the in game chat and add them after the match if you consider them good enough.
Play a few games with them to develop the in-game chemistry. After developing acquaintance with players, you may add them on social network such as Facebook, and call them to team-speak for a little chit chat session.
Keep increasing your popularity in the gaming community, and remember never flame online. As you get famous in the community, you need to be ultra careful with your behaviour. Even if you flame once or twice in-game, your impression will be ruined and players will not want to talk to you.
Create a name and logo for your clan. If you visit a local team speak server regularly, request the admins to make a private channel for your clan. After setting up the clan, play friendly matches with other clans to get a taste of competitive gaming.