"Stop judging by mere appearances, but instead judge correctly." That's what Jesus said in Judea way back in the day at the festival (John 7:24). After all these years folks are still judging by what they THINK they see in others.
I cannot count the times that someone has come to me and admitted that upon "seeing" me that they had some erroneous thoughts and negative opinions. Then, after watching a while, talking a while, walking a while with me they finally get it. There are three lessons in this:
#1 Our "vision" is clouded by our own perspective and experience. We can't always trust the way we see it. We see it like we have experienced it before and if we've never experienced it then we believe it not to be true. Truth is subjective and changes with perspective. Facts are not. Many times we ignore facts because we are an opinionated people. Instead, our truth is based upon our feelings or experience with the facts. So when we "see" someone who reminds us of someone else we say "I know that type" so we judge them a being a certain way. When we see someone that may appear strong at the moment, we judge them as being a person of strength. So on and so on...
#2 If you are faking it, people eventually know who you are on the inside no matter how you might cover it on the outside. The more time we spend with people and watch, walk, and talk with them, we begin to learn who they are inside. So it is futile to attempt to go through life with the mask on unless you plan to change relationships/friendships over and over again. Sure, there are times when you must guard your being, but in building relationships with others - friends, family, romance - you must be authentic and transparent. You might as well be, because eventually everyone figures it out anyway. Truth and transparency speeds the process to either break-up or live happily ever after.
#3You need to be certain of who you are on the inside so that no matter what others think or say, you know WHO and WHOSE you are. People are going to form opinions of you because its human nature. Most times those initial opinions will be inaccurate because they are shaped by past experience and subjective thoughts. It is important for you to always know exactly who you are at the core so that those opinions do not make you behave in a way contrary to your nature. Learn not to be put off by the inaccurate opinions of others,. Try to understand that it is not a personal attack of you but rather a personal experience for them.
It takes a lot of time and interaction to really learn who a person is in order to judge correctly. It takes years of work. You have to watch, walk, talk, and listen. If you don't have time for that then I think you should just stop at Matthew 7 before moving on to John 7 and "Judge not".