It is in my own experience that a true best friend will stand by you no matter what flaws or personal issues you may have or have been forced to deal with (unless you act as a complete jerk all the time in which case ... just to be clear I'm NOT CALLING YOU OR ANYONE ELSE A JERK. I'm SAYING DON'T HANG OUT WITH JERKS) Be someone you trust and don't betray that trust someone who will listen to you.
In particular, understand how you are acting and reacting, your various phrases, etc. They don't often misinterpret you Be patient with you when you make mistakes or have issues Above ALL else — be someone you care about and may even consider yourself a kind of second family and they will care for you just as I have very few true friends and it took me some time to figure out that my other friends aren't always so great... but that's besides the point.
If you find a true friend, do your best to make them as good as they do to you.