Psychology is not always relevant in every day life (but come on, mostly it is). But these are the little things I've learnt that have most changed the way I do things or believe things.
  1. P. T. Barnum effect
    Where people describe something and you go "holy shit that's me all over!" Eg. Horoscopes, psychic readings, etc. The P.T. Barnum effect is what happens when someone uses vague enough descriptions that they could really apply to anyone. "You have a change coming up. You're excited by it, but also a bit nervous. You like to be with friends but also like your own space at times. You make decisions carefully but sometimes like to be spontaneous." (<-- tell me this isn't you.)
  2. Smiling makes you happier
    Lots of people think physiological changes are caused by emotion. You smile because you're happy. Your heart pounds because you're scared. But actually, your heart pounds when you've seen a bear to prepare you to run away. Your body then interprets that as fear. You can use this trick - if you force a smile, your brain will eventually assume it's because you're happy. It doesn't even have to be a real smile, just raise the corners of your mouth. Trust me, I've lifted a bad mood with this before!
  3. Asking people for favours makes them like you more
    I don't remember the psychology behind it. But doing someone a favour often makes YOU like them more than it makes them like YOU. (So basically don't be afraid to ask for help. You're not annoying them (usually).)
  4. Fundamental attribution bias
    If you do something shitty you go "I'm sorry please don't hate me I'm having a bad day/got distracted/am super late". If someone else (esp. a stranger) does something shitty you go "jeez what an A-grade arsehole". Most of the crap things you do are situational rather than because you are a crap person, so I try to remember to extend the benefit of the doubt to the other person as well :)
  5. Self control is like a muscle
    So the more you practise, the better you get! ...I don't use this knowledge though, I use THIS knowledge: don't try to be disciplined at too many things at once because you'll tire yourself out. Your muscle might not be strong enough. Which means I always eat eighteen blocks of chocolate when I'm trying to study, with NO GUILT
  6. Women tend to underestimate their abilities
    By a while standard deviation. Ladies, you're smarter than you think you are.
  7. You can learn unconsciously pretty well
    Like seriously your brain just makes associations without you know. I used this when learning to drive - my mum tried to teach me what to look for to make sure I was staying within the lane, but I was like "nah mum, just keep telling me when I'm wrong and my brain will learn it somehow". It a hundred percent worked. (Also worked at freaking my mum out for the first couple of months.)
  8. If you're worried someone wants to kill themselves, you should ask them
    This feels callous or embarrassing or...insulting? Or like by asking, you will make them hide it more. But I have been taught that if you ask someone who is planning on killing themselves, they will likely tell you they are. And from my own personal experience, asking someone who isn't planning it does not offend. They might think it's ridiculous. But they will likely appreciate your concern. You can save a life with this.