Put a pic of a hot chick and what looks like a FB profile and you'll get a CTR of like 35%. LOL. Otherwise your CTR is gonna suck. The FB zombies don't like to click on anything that might take them away from their sheltered little sandbox.
Way to totally mislead a newbie.
So in answer to your question, a good CTR depends on what you're promoting and how good your ad is.
Forget CTR, think ROI.
Really? I've currently got a CPC ad that's converting at 0.1%, paying £0.15 per click. The CPM cost though, is saying around 50p per thousand, and the CTR seems to massively drop when I run it CPM. :SYou want to aim for 0.08% CTR at least.
Once you hit that you can start thinking about CPM..and even that is heavily based on what bid vs payout.
Do the math.