I have been thinking that these three simple words 'Mind your business' might be the key to having trouble-free interpersonal relationships at work and at home.
Minding your own business at work to me means,
(a) Staying focused on my responsibilities and self-improvement
(b) Not giving unsolicited feedback or advice to people - i have learnt the hard way that giving unsolicited feedback or advice to someone is always a very bad idea no matter how close you are to that person... only exception is when you are that person's manager or mentor. People in general know deep inside where they stand. They don't want to hear it from you. If you point out their mistakes, they'll get defensive and it'll only make them person shut you out
(c) Not telling people how to do their job - this clearly falls in 'trespassing' category and i absolutely hate when other people do this to me. So, this is definitely a no-no