Fuel injector cleaners that you add to your fuel to help a little bit in cleaning the nozzles on the fuel injectors and can help to improve performance and gas mileage a little bit, but if your fuel injectors are starting to get really clogged you need to have a shop remove the fuel injectors and clean them out manually to get even better performance.
Getting fuel injectors cleaned by a shop costs around $85.00 and it's well worth it if your vehicle is suffering from poor gas mileage or poor engine performance.