To easily take over warehouses and hubs, even compounds and just make the game a lot easier, don't try to take anything over right from the jump.

Start off robbing banks and carrying out missions until you aquire $400,000. It takes some effort and time but it pays off big in the end. Purchase the 3rd level shotgun upgrade (the Street Sweeper). Then feel free to do whatever you please. This is easily one of the most powerful guns in the game. It generally requires only one shot to do the trick but sometimes it can take two.

The easiest way to get the $400,000 is doing missions, but robbing banks helps to. The easiest way to rob a bank is to pay off the cop outside. Walk into the bank and strangle the gaurds. They don't generally shoot if they see you strangling a fellow guard, they'll hit you with their club. Once one has been choked, proceed to do the same to the others until they're gone. Blow the vault and get out as quickly as possible. Hurry to your safehouse and save your game. Try to do this as often as possible.

Once you have the money to pay for the Streetsweeper weapon ($350,000) it's smooth sailing!