The CF30 is essentially the FCA controlled function for those dealing directly with end clients, normally advising or similar, for those reading this who are not aware. There are other controlled functions such as the directors of the firm, head of compliance, anti money laundering officer, etc.
CF30 is normally pretty easy to get. There is no exam but they would normally expect you to demonstrate to the regulator relevant experience and appropriate qualifications. I've never heard of someone going and getting a CF30 on their own, it is by its very nature tied into the firm itself. You are carrying out the function to deal with the end clients of a firm, not saying you are able to deal with end clients and then go to any firm.
Once you have held a controlled function is is much easier to do it next time around, as Lord Flasheart implies. Basically you've already ticked the boxes and as long as you were not struck off for any reason you just go and do it again somewhere else.
Hope that helps!