never pay for media entertainment. pirate all movies/video games. don't go to movie theater, try not to be caught up in popculture worrying about discussing the newest game/movie, just do your own thing at your own pace.
never eat out at restaurants, except on very rare occasion (definitely not weekly, maybe monthly or 2-6x per year)
don't fall for the stereotypical chivalrous relationships where the man is expected to treat the lady. tell your girlfriend to buy her own shit, seriously you can end up paying $5-10k/year on a woman in needless spending and that's on the cheap side.
don't buy expensive snacks or luxury items at the grocery store, learn to be content with a fairly basic eating style, meat 'n potatoes sort of thing. many snacks are exorbitantly expensive for what you get out of them.
get on the cheapest cellphone provider you can, especially if you don't use your phone too much.
if you currently live alone, consider a roommate if you can tolerate one, cuts the rent/utilities/internet in half, huge savings.
try not to be caught up in social expectations regarding things like fashion. buying expensive clothes is kind of stupid unless you're really involved with that sort of social scene. if you're just some NEET/nerd type but have this obsession about dressing well, you're essentially wasting money.
don't go into debt on credit cards and then make minimum payments, interest rates are essentially just burning money. personally i have an emergency CC that i haven't used in about 5 years.
don't waste money on tech gadgets. be happy with a 6 year old cellphone, don't buy handheld gaming systems (or any gaming systems), don't buy fancy watches, in fact don't buy anything you don't need to survive.
Live as far below your means as possible, I'm talking 50% if you can. Save your money. You want like 1-3 years of living expenses in savings, enough that if you get fired from your job you'll suffer zero stress.