The way to promote bitcoin are posting in social media like Facebook twitter instagram and other social media about bitcoin and you can advertise bitcoin in some site and you can join in campaign to promote some businesa in the bitcoin.
Along with that the most effective and easiest way to promote bitcoin is to show your relatives and your friends and family that how you are earning with bitcoin and to explain them about all the features of bitcoin and to show them the benefits which will give them in the future so they will then adopt it and will invest in bitcoin. And after getting the benefit they will also do the same to invite other people to bitcoin.