To find a parking spot in Ballston, go during the daytime, avoid Wilson Blvd and Fairfax Drive, and consider parking in nearby Virginia Square, which has many empty blocks.
To park in Clarendon, good luck finding a spot on Saturdays between 11 a.m. and 8 p.m. Generally, there are more spots south of Washington Blvd but be on the lookout: spots can open up quickly as people do not stay parked in Clarendon for long.