Playing the stocks in GTA 5 can be a confusing and costly endeavour. While Lester's Assassination Missions are a sure thing to make huge amounts of cash after the main story missions have been completed, investing in other stocks can be a little hit and miss. You’ll need to keep an eye on the two in-game markets - the LCN and the BAWSAQ - to watch how prices are being influenced throughout the game. Just remember: Buy low. Sell high.