God takes the lowercase when used for a general deity and the uppercase when used as the name of the Abrahamic god. Thus May God bless you indicates a direct reference to the Abrahamic god, whose name is God, rather than any other possible deity. Do not follow this capitalization for God’s pronouns, which should remain lowercase (see he and him).
For some Jewish writers, God’s name is so holy that it may not be uttered or even written. Although this prohibition generally applies only to the seven sacred Hebrew names of God, faithful writers extend the restriction to the translated name God, writing instead G-d. This habit is unlikely to affect non-Orthodox writers.