A key suggestion to make the most of Tapping is to be as specific as possible about the issue.
As you tap you likely will uncover additional elements or new issues, which you can write down and tap through in a different session or if you prefer, you can work to clear the new element, and come back to your original topic. When you do try to rate the intensity and see if tapping on what came up cleared it, and if not continue to tap.
It truly is like peeling an onion! If things don't seem to be budging yet, then try to tap on a regular basis for at least 15 minutes and see if that helps.
Another great way to help increase effectiveness is to use the 9 Point Gamut technique. You can learn about that here: http://www.thetappingsolution.com/eft-articles/remember-to-roll-your-eyes-a-deeper-understanding-of-the-gamut-point-procedure/
You can also find more tips on common Tapping obstacles here.