At its most basic level, no doubt, it means that we have to complete our moral inventory, share what we find, and then get rid of the resentments, fears and remorse that have held us in bondage. We do this, in part, (particularly in respect of our resentments and remorse) through making amends where possible for the harms we have caused others. In part, we overcome our fears and remorse by engaging in daily prayer and meditation that lifts our thought plane to a whole new level. But is this all? If it is, it may be rather limited.
A second, deeper level to the admonishment to let go of old ideas comes into play as we realize that even new ideas become old very, very quickly. For instance, if a person cuts us off in traffic - a commonplace occurrence we are as likely guilty of as many times as is the person who cuts us off - how long does this action live on in our minds? Do we flip off the other driver? Do we need to comment on the alleged offense to our other passengers? Do we need to critique in depth the other driver's skill, motivations and character? Such thoughts gets old fast.
Take as another example being called into one's employer's offices for an annual review. All goes well, but as is the custom one's boss highlights several areas where improvements might be made. Do we seethe or worry over these constructive criticisms and allow them to haunt us for weeks or months? Or, do we take them in stride for what they are? If we allow criticism to fester inside of us, how quickly do such new ideas become old?
Thus, on the subtlest level, holding onto old ideas forestalls all spiritual growth because it reinforces our old thought patterns, and such old thought patterns (of course) are synonymous with our character defects. That is, if a man consistently thinks angry thoughts he becomes an angry man, consistently thinking jealous thoughts makes for a jealous man, and thinking envious thoughts breeds envy, etc.
One suggested methodology for getting rid of our old ideas is for us to raise opposite thoughts. Thus we are told to think of a person who harms or offends us as being a sick person. Raising thoughts of compassion for the seeming offender, we dissipate the judgmental thoughts that would otherwise separate us from that other, and more importantly separate us from God. Similarly, if we are patted on the back for some good that we have done others, we are advised to take this humbly in stride, knowing that we were merely acting as the agent of God's will for us.
The choice is really, thus, to let go of our old ideas and to realize God in action, or to hold onto our old ideas and suffer in the bondage of self. And, it is this bondage - the "painful inner dialogue" of the ego - that is the source of all suffering. Selfishness and self-centeredness, we are told, are the basic root of our problem, and we must be rid of (or at least reduce at depth) this separated sense of self if we are to live fully and fully recover from our alcoholic addiction. To do so, we must absolutely let go of all our old ideas no matter how deeply or lightly they may be entrenched.