After lots of mistakes, handful of regrets but vivid experiences ,I have tried to establish some ground rules which I myself try to abide by

Never insult you parents : They have gone through a lot to take care of your needs. Eventually they will need you to accompany them through their difficult times
Do not invest too much on temporary relationships: I mean your capital and time. It wont give returns nor it will be remembered
Never involve a third person (esp a family member) in your relationship nor get involved in someone else’s. This has a high chance that the ‘outsider’ will ultimately become the ‘negative one’
Do not get afraid to take risks in your 20s. If you have passion for business, go for it. If you want ‘respectful’ job, there is UPSC.
Never disrespect anyone. I Repeat ANYONE. Even the person who hurt you the most. Maintain your dignity
Never try to control your laughter (unless the situation is utterly grave). Laughing definitely helps create a positive aura
Never take calls with alcohol. Do not touch your phone while taking liquor. You might end up hurting someone
Do not overthink. It just messes with your already complicated brain and cause futile losses
Never go to an engineering college fest just to meet girls. There is a high chance you end up alone
Never lie to your sibling. S/he understands you the most and can get you out of any situation
Never try to read everything for your exam (obviously unless you want to top the ranklist). Just first try to focus on previous year questions and read accordingly
Never try to flirt with your teacher (howsoever hot she is). She can get you say sorry in front of the whole assembly
Do not open quora just a day before your exam. You might end up with another mistake of your life