One of the most common mitigation techniques is ASD. With this process we drill a 3' hole in the foundation floor for the suction point with a Radon Fan on the exterior. Some homes do require two or more suction points.
HRV's are another method for radon mitigation. This works great for homes with stone foundations and/or dirt floors and crawlspaces.
Many newer homes from the early 2000's and on may have a passive system already. If the levels are still high we just need to install a fan in your attic.