your objective is obviosly to take over miami you can do this by

getting drugs:your dude who gives you leads will tell you where there are drug dealers but to make a deal with them 9 out of 10 times you will have to do something for them once you get the drugs and sell all that you have make sure to put all the money in the bank you wouldnt want to lose it all would you?

steal cars: the dude who gives you leads can also tell you where there are cars that are worth alot however when you steal them sosa or however owns that turf can send their minions to go and destroy your car

take out gangs: there are many gangs in miami and killing them will not only give you their turf but you get all the money and drugs they have there.

buy stuff: if you have some money you can upgrade you safehouse to a mansion and fill it with furniture of your choice you can hire minions to protect cars and go earn money for you (make a profile for them as well)

make allainces: mabye you dont have enough guns or minions to take over a certain place go make some friends wit other players they may help you take some turf but they might have conditions that need to be made before they ally with you if an ally helps you take over a turf the profits and drugs will be split unless one of you buys the other person out