Watch the Add Muted Strums online guitar lesson by Vicki Genfan from Acoustic Rhythm Guitar Cookbook
You might want to practice changing from the C to the FMa7 chord a bit before going into the strumming pattern. The movement doesn't have to be big – just accurate! Start slowly and work up your speed as the change gets easier. To get the "muted" sound, just let your hand fall back, naturally, onto or near the sound hole. Your hand should be relaxed, if possible.