Here’s my strategy guide that came across on Agen PKV for levels 13-24 in New York for Mafia Wars.
Jobs: Now you can (or will be able to) do jobs from the first 5 job tiers (Street Thug, Associate, Soldier, Enforcer, amp; Hitman). There is a lot of high paying and high experience in rewarding jobs. If you want to get the maximum amount of money from doing jobs then do either Wiretap the Cops (Enforcer) or Exterminate a Rival Family (Hitman). If you want to experience jobs then do either Wiretap the Cops (Enforcer) or Exterminate a Rival Family (Hitman). In order to do some of the higher-paying jobs, you will need to make some large investments in inventory.
Now you can start to buy some more expensive (and higher-paying) properties. The Tenement is a nice starting point to invest some of your money from jobs, because it is like a Mega Casino, but pays less. When you upgrade it a lot it will start to make you a lot of money though. You will probably be able to get most, if not all of the properties. I got the Mega Casino during this time, so it is definitely possible for you to do it as well. At this point, you will begin to see that the sky is an understatement of the limit of how big of a money maker your properties can become in New York!
Now I suggest buying anything that you need for doing jobs, as well as getting achievements (such as Armed Dangerous, requiring possession of at least 10 Tommy Guns). But whatever you want, at this point you are beginning to become super-rich. If you want to you could buy a million (yes, 1,000,000) crowbars or baseball bats just to waste money.
You will have earned a total of around 150 or so skill points at this point (at the least). If you want to do most jobs then go ahead and pour all 150 of them into energy. If you want a lot of skill points then try to master all of the job tiers, each mastery will earn you a total of about 20-30 skill points! If you want to be a fighter then (with a large and powerful enough mafia) put most of the skill points into the attack and some into stamina. If you want to be safe from attackers then put most of the skill points into defense and health.
Now you can start to attack other players. Make sure that you don’t have a ton of money on you when fighting because you will risk losing it. If you want to hunt for bounty then get some of your friends to all sucker punch the player on the bounty list. If you are going to sucker punch the player until they are iced them make sure that you have at least 100 stamina or so, you can deal out a few hundred damages before running out!