Finding the Quiet by Paul Wilson is a thoughtful guide to mindfulness meditation. In the second chapter, the section called "The art of letting go" offers the advice:

... be prepared to allow things to happen at their own pace. Without applying effort. Without trying to analyze in any way. And without expecting any particular outcome.

Wilson expands upon these themes:

Without effort ...

... So get used to the idea of doing nothing, applying no effort, and just allowing things to happen and unfold in their own good time. However long it takes is exactly how long it's meant to take.

Without analysis ...

... As human beings we are desperate to rationalize and find the meaning in everything. But there is no meaning to be found in the act of meditation. Its purpose is just to still the mind so you can observe what is real. ...

Without expectation ...

... you are not using your practice to attain something, because the practice itself is the attainment. Impatience vanishes. You have all the time in the world.

(cf. Jon Kabat-Zinn commentary This Is It (2008-11-14), No Method (2010-01-21), Dimensionless and Therefore Infinite (2010-02-03), Being with Your Breath (2010-02-20), ...) - ^z - 2010-08-04