A Few Easy Achievements
To easily get the 'Walk Free' achievement, go to the airport and drive on the airstrip. Head north until you find northern exit of the airport. You should be able to lose your 4 star wanted level quickly.
Once you are able to freely access the second island, take a taxi ride from the first island to the second island without skipping to unlock the 'It'll Cost Ya' achievement.
For a simple way to unlock the 'Chain Reaction' achievement, enter the Weapons tier 1 cheat "4865550100" into your phone to get an RPG. Find an area (try a freeway) where traffic comes to a stop. Park your vehicle in the front and possibly a few others to cause a road block. Once there are ten vehicles, shoot the RPG at any of the vehicles in the road block to start a chain reaction.
More tricks, tips and cheats for this game are right here - Grand Theft Auto 4 cheats
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