The best and most effective way of air sealing your home is to a hire a contractor that uses a Blower Door and a Thermal Imaging device to determine where the leaks are.
Using the Blower Door will reverse the airflow and instead of pushing out heat it will bill pulling in cold through all of the cracks, seals and under-insulated areas. Then the Thermal Imaging camera can physically see the leakage points in your home.
This can not only save you time but can also save you thousands of dollars in repairs that may have not have been needed.
Blower Door and Thermal Imaging Camera
The below pictures show missing insulation in the ceiling/wall that would not have been detected with out the use of Thermal Imaging.