You should always start out your Facebook campaigns with CPC. With CPC you can much more easily control your per click cost. Once you have some conversions and know your audience and are relatively intimate with your approximate CPC, you should switch to CPM to increase your exposure. If you just jump feet first into CPM, you can lose craptons of money in short amounts of time with no return on investment. You need to know your numbers. You don't have to worry about all the numbers in between. Yes, you should look at them and yes, you should evaluate them, but the number that you should most focus on (and this is very important) is how much you spent to acquire a sale. Did you spend $50 to land a $100 sale where you get paid a 75% commission? Or did you spend $10 to make a $7 sale? It all comes down to your return on investment (ROI). It's much easier and much more important to display your ads in front of a targeted audience than it is to get cheaper clicks. Cheaper clicks are exactly what they say they are -- cheaper clicks. That's it. There's nothing special or different about them except their cost. But! A more targeted audience is more clicks that convert to sales, and therefore a larger ROI. You should never stop testing your ad. You should never, never be satisfied with your ad. 17% conversion, wow, that's awesome! Can you get 17.1? You'd be amazed at what one tiny little thing can do to increase your ROI. Good luck.