When you get a tip from an informant about the price of any drug going up, stock up on that one drug. Buy it from different locations. You will need a car. Muscle cars allow you to get to about three places in a day. For example, if you hear that weed is going up in the Bronx, buy as much of it as available from all locations (or until you are out of money) and sell it the next day. The more product you can get, the more profit you will make.