Originally posted by DEREKTROTTER
Heres my tips:
Dont do any Assassination missions until you've completed the story
You can get easy money after each of these missions, there are hints in what to invest in: Just put all money on and sell after mission
Random Encounters
If you are driving along and notice a blue dot appear on map, help the guy out and usually they give you tips for investing on the market. Again, just put all money on their tip and sell for profit