This a tip for noobs when your making large deals stay away from places with low populations, only high populations have the oppurtionity to make large sums of money.

another way to make a lot of money is travel to places with low populations, buy cheap drugs there, and sell them for high profits in cities with large populations. If you didn't already know this, this is how I make money really fast and with relative ease of use.

another tip in the beginning: do never buy to many drugs at once... that rises the prices... same happens if you sell to much at once

Set yourself a target when buying and selling drugs.

For example:

buying drugs
only pay for drugs at a rate of under $20 per gram

selling drugs
only sell your drugs at a rate of over $60 per gram

with a fixed system like this. you will always know whether to BUY or SELL your drugs when you arrive in a city.

NOTE: the above is just an example. after visiting a few cities you will be acustomed to the prices of the drugs. and know what targets to set.