Yeah. That's right. I listed it. It's true. You want to make some money in GTA, the very first thing you're going to have to do is prevent yourself from spending your hard earned/stolen money needlessly. Sure, you're going to need weapons to be able to succeed in the game, but you won't need half of the weapons available to you at Ammu-nation. Stick to one of each type and move on. Same thing goes for clothing and hair styles. Agreed, customizing the characters to fit your internal stereotype of them is great fun, but thus far, I see no benefit to having several unused outfits sitting in a closet. If you're reading this guide for the purpose of being able to afford more clothing for your characters, I think you may be missing the overall point of this game.
Just like the real world, those worth the most, have a large portion of their funds diversely invested in the market. If you hope to attain any acclaimed level of control over the city of Los Santos, you've got to entrust your funds into those that make it run. If you're looking to make some dough fast, you can always try your hand at day-trading, just remember that short term investments are far more risky. There's also the option of making money with the Time Traveler method, which is done by taking note of the stock prices (by either taking a photo of the screen with your phone or using a pen and paper), saving your game and then letting between 4 to 8 hours of game time go by. Check the stock prices again and write down the companies whose stock prices have risen. Go back in time by reloading your save game and invest as much as you can into the companies that you know will earn in the next 4 to 8 hours. Voila! Fast and easy money!
Disclaimer: To make the most money possible from Assassinations, execute the first and ignore the rest until after you've completed story mode.
Dying costs money. Every time you die in GTA 5, the hospital has to re-clone your body, dress it in new versions of the clothes you were wearing at the time of death and transfer all memories from the corpse to your new body. This stuff, while far less expensive than it would be in the real world, isn't cheap. Thusly, if you want to make more money, stop dying.
Common criminality at its best. If you find yourself just a few hundred short of being able to make a purchase, easily solve your shortage by heading to the local convenience store with a weapon drawn. Point your crosshair at the clerk and wait for them to empty the register. If there are multiple registers, shoot the others open once the clerk has finished emptying theirs and run. Small type robberies like this will still result with the police being called, so be prepared to run and lose the cops once you've got the cash in hand.
Chop. Lamar and then Franklin's dog is one loyal, horny and sadistic pooch. Not only is he good for attacking anyone you point your cross hair at and sending you annoying notifications about his hunger in the iFruit app, but Chop is also useful for sniffing out treasure and other collectibles. When not on a mission, head to Franklin's backyard and take a stroll around town. If you do this for 10 minutes without him finding anything I'll… keep living my life as though I never said this.