The first thing you need to do is not use generic words. If your call to action says “buy now” people are less likely to convert compared to if you used a benefit driven call to actions.
For example, on my site, which is about marketing, my call to action text is about “increasing traffic”.
Also when you use images on your website, especially if it is images of people, their eyes should be looking at the call to action. This way people focus their attention on your call to action.
If you also add time sensitive words, such as “today” or “free trial” or “grow your traffic today”, you are more likely to get more CTA clicks.
And last but not least, make sure you place your call to actions in the right places. Look at where people scroll using Crazy Egg, and make sure your call to actions are in the right place.