Never fight anyone's battles if they've never fought yours.
Never let anyone hook you up with a partner. Find one yourself if you even want to be in a relationship.
No one is loyal any more.
Don't listen to anyone who claims they will help you through life. If anything, they're the first ones to stab you in the back and throw you under the bus. Help yourself.
Not everyone who smiles at you means well.
Leave religion alone.
Never give your all to a person no matter who they are.
Just do you and don't worry about what other people think.
Deal with your personal problems yourself and never talk your business. If you need to do that speak to a counsellor/therapist instead.
Even most family members cannot be trusted. Most of them are just people who happen to share blood and nothing more.
Learn to be indifferent towards anyone and anything. It's kinda sad to be that way but it's just the world we live in.
Don't let anyone know too much about yourself. They'll use it against you later on down the line.