Before going into fights, research your opponent before pressing the attack button. Just do a quick run through to see how powerful the player is...

First, look at the size of the player’s mafia. I always tried to attack players with nearly the same size or smaller mafia as I have because more members means more weapons that will be used against you.

Second, look at the number of jobs, which will give you a sense of the player’s experience and how his profile points are distributed -the higher the number, the higher the probability that their attack and defense is strong. I usually attack players with about the same amount of jobs completed or lower.

Third, look at the number of wins and losses that your prospective opponents have. A higher loss to win ratio offers you a better chance of defeating them.

Fourth, quickly browse through the player’s weapons arsenal. If you see that they have much stronger weapons than you or a large quantity of stronger weapons, it is best not to attack them.

Fifth, look at the player’s properties to get an idea of how much money they possess and how much they can be robbed. Gaining money from attacks is good but not always necessary. Winning attacks earns you experience points at a fairly steady pace without wasting any energy. Often times, I will earn a few hundred thousand dollars off of an opponent and then keep earning experience points after they are broke.Once you find a good candidate to attack, test them out with an attack. If you lose the first
fight, move on to another player to attack. If you win the first attack, take advantage of it and repeatedly attacked them until you are out of stamina or you lose a fight. It’s unrealistic but,
mafia wars lets me win repeated attacks on a player and then suddenly gives me a loss...

If you keep winning attacks against a player and you run out of health points, keep the attack window open until you earn more health points. I usually open a new window or tab to the game where I can restore my health and deposit money or do jobs without interfering with the player that I want to keep attacking. Once you earn enough stamina or restore your health, go back to attacking the player until you lose. One other thing I learned about the health points is that you can pay the doctor to restore your health with the money that is in your bank account, so there’s no need to keep money at all in the cash box. 

Create an attack list of those members that you have attacked and beaten. This way you can go back and attack them again in the future, knowing that they are probably beatable again to you. Using Mafia wars, you can’t just keep track of them or look them up later, at least not to my knowledge. Instead, right click on the name of the member and copy the link location. When you’re ready to attack again, simply paste the link location to the member’s profile into the navigation bar of your browser.

One warning, though, is that there’s always the chance of the members, we have attacked repeatedly, will seek revenge at some point. Either they will grow stronger and attack you later or they can put a hit out on you using the hit list and get other stronger members to take you out. You need to weigh the factors involved and, whatever you do, try not to get a really, really stronger member mad at you!