Man, no one is willing to be straight forward and helpful anymore. Best thing to do is just like the real market- buy low and sell high. The stocks that have seemed to go down and up consistently are Hawk & Little, Pisswasser, and Whiz. If you see one for a few dollars a stock, pour money into it and then sell when it goes back up.
For instance, Pisswasser was at $4 a share a few days ago. Now it's up over $44. So if you had purchased $10,000,000 of stocks for each character, and sold it now, you would get $110,000,000.
Remember that each character is separate, so you can diversify or invest n the same thing with all 3. Good luck!
"Oh but if I went 'round sayin' I was Emperor, just because some moistened bint lobbed a scimitar at me, they'd put me away."