[video=youtube;uCNqdIezHeA]http://www.youtube.com/watch?v=uCNqdIezHeA[/video]
But seriously...
1. Get your own pad and start growing! Buying top shelf bud is bullshit. It's so easy to grow that a cave man could do it. If you want to fire up a couple ounces a months of high grade sinsemilla then you should own your own place. It makes more sense financially than any other living situation (with your rents, with roommates, renting shitty apartment, etc). Why spend $400-$600/mo on bud, when you could just spend that on a mortgage and grow your own? Then you own a house too. I was hesitent about buying my house, but i'm so glad I did. It's the only way to go.
2. Trust no one. I talk to almost none of the people that I was tight as brothers with back in the day. They betrayed me. My gf cheated on me, my best friend fucked my gf - in my other best friends bed, i've had friends steal, i've had family members steal. The only person you can truly trust is yourself. Live your life, but be cautious because most people are terrible.
3. Avoid debt. Don't buy anything you cannot pay cash for. Obviously it's not possible for all situations, you will probably need a loan for a house and for a car at some point, but even those debts should be avoided if possible. Use credit cards, but only buy things you already have the cash for, and pay off your cards in full every month without exception. My credit is through the roof by filtering all my purchases through a card, and I have never paid interest on a credit card and I never will. This advice was given to me, and seems obvious, but I see almost everyone I know NOT follow it with disastrous results.
EDIT: And to go along with the personal finance, make yourself a rainy day "shit happens" fund. Insurance goes up. Shoes fall apart. TVs die. Computers die. Lawn mowers die. Cars die. Tires degrade. Hot water heaters die. Air conditioners break. Furnaces need replacing. Windows break. Roofs eventually need to be redone. This shit happens. I know a lot of people that bitch and moan and complain about how this car repair, or the furnace going out set them back and caused them to put $$$ on a credit car and put them into a hole they can't crawl out of. My next question is why they didn't have a "shit happens" fund and why they aren't starting a "shit happens" fund for the next thing. Just keep 2-3 grand aside just in case. The worst case scenario is that nothing breaks and you have extra money set aside, which really isn't a bad thing. Eventually though you will need that because shit does happen.