You might think that one call to action on your landing page for your pay per click advertising campaigns is enough. You’d be wrong. It isn’t. What’s more important is that your page visitors see your call to action at least three times.
Yes, three times. You need one call to action above the fold so it can be seen upon landing on the page. This one thing alone will reduce your bounce rate. When visitors see that call to action they will want to know what it is they are supposed to buy. So they will read the page at least down to that first call to action and a significant number of page visitors will make a purchase – if your above-the-fold sales copy is solid – on that first call to action.
Somewhere in the middle of the page – one-third to half-way down – include your second call to action. This call to action will be for those people who need more information, but they don’t want to read your entire sales page.
The final call to action, of course, should appear at the end of the page. This is for those people who need to read a lot of information before making a purchase.
Three is the minimum. You should have a call to action visible at every scroll on your page. Looking from the top to the bottom, if I land on the page then the first call to action should be above the fold, visible on the first landing. When I scroll down to the beginning of the next section, just below the fold, then I need to see another call to action. When I scroll to the next section then I need another call to action. You should repeat this process up to seven times. Your landing page for your pay per click campaigns should have anywhere from three to seven calls to action. Watch your conversions grow.

Nick, interesting insight. I agree with you in principal. It makes sense to have a call to action per every scroll. Do you know of any studies that showed the effectiveness of the increased number of calls to action?
Studies? I don’t know of any published studies off hand. Just personal experimenting and discussions with other PPC advertisers led me to this conclusion.