As a functioning human being, relationships with other people are enormously important. In Abraham Maslow's Hierarchy of Needs, social relationships are the first level of psychological needs, the first tier after our physical needs. According to Maslow, after we've achieved our "Belonging and love needs" (intimate relationships, friendship, etc.), then we can move on to the next tier, which is "esteem needs" (prestige and feelings of accomplishment). If we make it out of that alive, then we're ready to prepare for self-actualization, with is achieving one's full potential.
To a certain extent, we could argue that our need to belong socially and our need for self esteem are a bit of a chicken-and-egg complex. However, if you want to have the best relationships with others, you need to have the greatest relationship with yourself.
Here are ten reasons why you should be your best relationship:
1.) You are incapable of understanding how someone can love you, until you understand to love yourself.
2.) You are less likely to lose yourself in other types of relationships.
3.) You learn to let go of the self doubt that can prevent you from experiencing other relationships.
4.) You understand your wants and needs, which leads to less experimentation and potential disappointment.
5.) You stand up for yourself and don't allow others to treat you any less than you deserve.
6.) You can be kind and compassionate to yourself, in ways that people on the outside might not understand - and that you might be unwilling to explain.
7.) You validate your own feelings and experiences without needing an outside party to provide such.
8.) You can be comfortable in being alone.
9.) Understanding your limits, and your comfort zone, you can practice pushing yourself to go further in a safe way.
10.) Excluding a few, the vast majority of people in your life do not stay in it forever. You are you for your entire life, birth to death. That's a long time to spend with someone that you don't have a good relationship with
In the end, it's probably every cliche you've ever heard. But there is a singular truth the the idea that the only way to know others, is to know yourself. Once you're able to understand, love, and be good to yourself, those feelings and actions are naturally applied to others in the best practice.