A phrase or a word for not practising what you are preaching

If you really believe in practicing what you preach, but periodically or for an extended period of time you openly fail to practice it anyway, then I suppose that your conduct can be distinguished from hypocrisy, which Merriam-Webster's Eleventh Collegiate Dictionary (2003) defines as

a feigning to be what one is not or to believe what one does not; esp. : the false assumption of an appearance of virtue or religion

Instead, you might refer to your conduct as straying, in the sense of the Eleventh Collegiate's definitions (f) and (g) of the verb stray:

f : to wander accidentally from a fixed or chosen rout g : ERR, SIN

or lapsing, in the sense of the Eleventh Collegiate's definition 1(a) of the verb lapse:

to fall from an attained and usu. high level (as of morals or manners) to one much lower; also : to depart from an accepted pattern or standard.

You might even refer to yourself (for Biblical resonance) as "a prodigal not yet returned."

For these alternative terms to describe your situation more accurately than hypocrisy does, however, your conduct and your intentions must satisfy several crucial conditions: (1) an absence of feigning or false appearance, (2) a genuine belief in the rightness of the practice you have preached, and (3) a longing to return to proper practice that is strong enough to draw you back from your straying, lapse, or prodigality. And even if you do pass muster on those three criteria, if you continue to preach what you have ceased to practice during your period of erring conduct, without acknowledging and condemning the gap between your theory and your practice, the term hypocrisy still seems highly applicable to your situation.

At the level of everyday office procedures (for example), it might seem too harsh to characterize a boss who makes everyone else submit TPS reports with cover sheets but declines to follow that policy him- or herself as being hypocritical. But it certainly isn't too harsh to say that such a boss has a double standard. Again, from the Eleventh Collegiate:

double standard 2 : a set of principles that applies differently and usu. more rigorously to one group of people or circumstances than to another ...

Consider the phrase or saying:

"Do as I say, not as I do."

I think sanctimony ( sanctimonious) can fit the context you are describing:

• feigned piety or righteousness; hypocritical devoutness or high-mindedness.

Or as a more general term:

Janus -faced:

• marked by deliberate deceptiveness especially by pretending one set of feelings and acting under the influence of another.

Source: www.thefreedictionary.com

CYNICAL

CYNICAL (the OED) adj. Concerned only with one’s own interests and typically disregarding accepted standards in order to achieve them: "Some people regard the governor's visit to the hospital as a cynical attempt to win votes." "A cynical manipulation of public opinion."

INCOHERENCE and INCOHERENT

"Coherence can be measured by the shortest distance between what you say and what you do."

Incoherence - "The quality of being incoherent." http://en.wiktionary.org/wiki/incoherence

• Coherent – logically connected; consistent. "The same rambling, incoherent manner." http://en.wiktionary.org/wiki/incoherent)
• Incoherent - Lacking coherence. http://dictionary.reference.com/browse/coherent

Other choices might be "inconsistency" and "inconsistent". Inconsistent or incoherent behavior.