Tips for Zazen (application of dependent co-arising)
There are principles in Buddhism that have helped me a good deal in zazen practice. These principles may also help others.

It is inherent in the Buddhist principle of dependent co-arising that nothing is self-powered. All things are brought about by causes and conditions outside of themselves.
Practitioners may criticize themselves for getting pulled away from their focus on breathing by worries about the day’s experience, fantasies about the future, thoughts of all kinds. All the time, however, the practitioner has no responsibility for any of the clamor that enters the mind. Just as everything else in existence, the meditator is not self-powered. That bothersome internal tumult is brought about by causes and conditions in his or her own mind that he has no control over.
A meditator may verify this non-responsibility by observing his own mind. For anything that enters the mind, the meditator need only ask, “Did I ask for that to be there?” The answer will always be “no.” So if one is thinking of eating mashed potatoes for dinner, there is the thought about it in the mind to be sure, but one didn’t ask for it and has no responsibility for it.
There is another idea that might be helpful. Since nothing is self-powered in the universe but is brought about by causes and conditions outside of it, nothing can be other than it is. Things just as they are, are absolutely right. They can’t be any other way. So as a person sits in zazen, whether the session is troublesome or peaceful, he or she can reflect that whatever is going on is absolutely right. You can sit in peace no matter what is going on inside of you. Everything going on is right.