(This post is written assuming you’ve got a decent amount of conversion data over a good enough period of time. I can’t define that for everyone, you’ll have to decide what’s good based on your industry.)
Here’s a simple way to reduce your cost per conversion and improve your conversion rate.
In your AdWords account, click on the ‘Dimensions’ tab on the Campaigns page and and select ‘Hour of day’ from the ‘View’ drop-down menu.
Once you’ve done that, you should have your conversion data broken down by the hour.
Sort this data by cost per conversion. Now, look at the top 4 and bottom 4 hours. If you notice a pattern, then go to the Campaign setting tab and adjust the ad delivery schedule so that your ads don’t show during those times.
You should see a reduction in cost per conversion in a week or so.