that totally depends on your site, niche, where do traffic come from, and how is your ad placement. what is your site url?
First, you should never disclose your actual CTR as it violates G's TOS. As for what a good CTR is, it depends on many, many factors. Certainly the source of your visitors is key. Search engine hits tend to increase CTR, and I've found searches from MSN to be the best when it comes to CTR. Also, what other options do your visitors have to leave your site besides adsense? Of course, you should experiment with placement, size, color and so on using G's A/B testing tool. I've found that with some minor changes, you can increase CTR substantially. But what works for one site might not work for another one. Age of site is also important. For the first six months of my site, I made very little. This month my adsense revenue is twice what it was last month and 20 times what it was just three months ago.
I would be happy with 1% which I had, now it's 0.3% I have more than 3 000 page views daily, once a week +17 000 (entertainment niche)