What clan should I join?

depends what you wanna do in this game and what skill level you are at.

than i would suggest joining a pub clan, you'd be surprised how much you can learn from just pubbing. it will get you used to the maps of CF and gets you to experiment around with some guns.

a pub clan is a clan that does public games together alot, opposed to scrimming ( clan warring )
there is 3 kinds of clans in this game:
pub clans - these clan aim to get to a high rank and pub alot
scrimm clans- these usually have less members and consist of mainly clan war players
farm clan- "power leveling" clans (terrible idea to even think about joining any of these)

hope that helped.