Whereas the philosophy that all we can know is what is in our own minds is often ridiculed as being impractical because it denies the objective existence of others, there is practical value in noting that our values and judgments are indeed subjective and thus changeable.
Our minds hold a pattern, which ostensibly corresponds to an "external" reality. It is a map of a territory that we can never sense directly because sensing necessarily filters information. If we had a direct, unfiltered experience of so-called external reality, we would receive one huge chunk of information, unorganized and unmanageable. It would be like downloading the entire content of the Internet as one large stream of ones and zeroes without a method of decoding it.
Objectivity is consensus and relative repeatability mistaken as fragments of absolute truth. The illusion of absoluteness leads us to a problem in judgment of right and wrong in human intentions and behaviors. When we think, "He should have done this," or, "She shouldn't be this way," there often arises an uneasy feeling of annoyance, rejection, or distaste. We automatically blame the other person for causing this disturbance when it really is our mind's signal that we are encountering a contradiction in our mental map of the world. Before we can even consider that our map needs correcting, we must be open to the possibility that our judgments are not absolute.
The feeling of judgment signals a contradiction between what we expect the other person to do and what we observe them doing. Ironically, it's easier to assume that our expectation is more correct than observed reality. This is simply a habit, a repeated pattern of thinking that has served us in the past. We ignore the fact that it does not serve us now out of sheer laziness: it requires thoughtful effort to adjust our mental map of how the other person should act. We would need to ask ourselves why it is the most beneficial course of action in their minds and hearts to do what they just did that annoyed us so.
What can we control?
A practical solipsist does not deny that his values and actions affect the conditions of his experiences even if he denies the metaphysical independence of such conditions. The practical question then is, "What can I control to achieve happiness or less disturbance?" In the case of judging people, the answer is to elaborate upon or otherwise change your model of how the other person should be. In other words, justify their behavior with adjusted "laws of the universe" (mental model). The alternative is to resist your observed reality, a tiring and futile endeavor.
As a bonus, when you understand more deeply and more consistently with your observations why a person values or acts a certain way, you can more easily organize causes and conditions for them to act in a way that is mutually beneficial. You can spend your energy where it actually matters instead of just frustratingly grinding on why they are the way they are.