There are many Achievements and Trophies in Watch Dogs which can be easily achieved with some quick tricks. Here is a guide on how you can get the Black Hat Trick, Magic Smoke and Free Radical Achievement/Trophy, with easy descriptions.
Black Hat Trick
All you have to do to get the Black Hat Trick Achievement/Trophy is kill three enemies with one IED, you can do this against any type of enemy, including police. The easiest way is to start shooting randomly at the civilians till someone calls the police. When the police cars arrive, throw the IED between two police cars, then time the explosion of the IED in such a way that it goes off before the police can get out of their cars. In this way you can target atleast four police men with a single IED. You can buy the IED’s at Tobias’s Shop for $300, which is located in the Loop District.
To achieve the Magic Smoke Achievement/Trophy you must acquire the “Focus” skill from the Combat skill tree. You will have to kill four enemies while focusing, in one go. Try to kill four cops when focused. Shoot randomly at the civilians till someone calls the police, when the cars arrive, aim at their windshield and activate the focus by pressing the right stick. Now shoot as fast as possible.
To get the Free Radical Achievement/Trophy you must escape the level 5 police chase. Shoot randomly at the civilians till someone calls the police. Shoot at the police reinforcements till you reach level 5, you can see the level at the bottom right corner of your screen. Now try to escape from the police in your usual style.