If you're not a "casual" just skip to standard. You can farm the easy mode boards out to the AI if you want to unlock everything (set to out to lunch). The way if you usually play is try to get at least 3 properties in a district, buy at as much stock as you can there then start investing in those properties. You can freeload off other players investments by buying stock in a district you'll think they'll invest in (if they get domination in one its a safe bet). Sales are the least important part unless you aim to bankrupt so less luck involved.
A few things about the stock market. Price goes up 10% when buying 10 stock or more a turn and goes down 10% when selling the same (if it doesn't it because of rounding i.e. 8.6 to 9.4 price will remain at 8). A 20% dividend of the sale is distrubuted evenly to stockholders of that district e.g. you and another player own the same amount of stock you both get 10% of the sale. If no else owns stock in that district keep at least 5 stock to get the full dividend (10 if you want to grief anyone else that might buy into later). Vacant lots are simple. Use ballons instead of real estate agencies (better effect if they land on them and don't have to renovate once all vacant shops are bought), circus sale prices are 100G upgraded to 500,1000 and 2000G each time you land on them (each upgrade increase shop value making it harder to force buyout) and 3 star shops increase stock value and can be invested in. Buy 99+ stock, renovate to 3 star shop, sell stock, renovate back to desired building is a way to some quick $.
This wall of text will make sense after you played a game. An easy way to get stamps is to play online (100 stamps per game +10 if you win) if you can someone to play with (usually Japenese in my experience).