Everybody Is Biased, Even You
You want to know how the other person thinks so you can place yourself in a position where you benefit from that understanding. But you already possess that knowledge, and yet you fail to use it. Most people operate in broadly similar ways on the surface. There are patterns that are almost universal, and still you choose to ignore them.
The best way to read someone is to read yourself. How do you make choices? What goes on in your mind? Answer truthfully. Be absolutely honest with yourself. If you are self-aware enough, you will begin to understand how opinions are formed and why we tend to share only our better thoughts with others.
You need to remember that you are not entirely unique. The other person is likely thinking in a similar way. The processing may differ, but the underlying emotions and biases are often alike. Once you understand how you arrive at your decisions, you can begin to see how others arrive at theirs.
Every person operates from bias. There is no one without it. Anyone who claims otherwise is not being truthful. Ask yourself: if you had to choose between two of your friends, whom would you pick? You already know the answer. Whether you choose to express it depends on what you believe is the right thing to do.
Knowing that everyone operates from bias, what should you do? Learn about their personality by observing their choices. How do they make decisions? Do not focus on what they say. Most people say what sounds right, what others want to hear. Personality is not revealed through words, at least not the true one, but through actions.
Observe how they move through life. How do they make selections? What justifications do they offer, if any? Categorize their choices according to underlying biases, and you will begin to see how they function. The goal is not perfect accuracy. You only need to identify the most likely bias driving their behavior, whether in relationships, work, or argument.
Once you understand their probable biases, you can realign yourself in a way that appeals to them, if you want them to think highly of you. It is easy to complain that people are not doing the right thing, but people have rarely acted based on what is objectively right. They act based on what feels right, and when the two happen to align, it appears moral.
As long as we have emotions, we will have bias. You can either use your emotions to complain about the biases that worked against you, or you can choose to realign yourself strategically to benefit from them. Complaining will not get you what you want. Strategic thinking might.