For an example,
If you are marketing for a photography social media then write a caption like this. "If you guys shared this post and which five persons get so many likes will be selected as a winner and they will get a privilege to get a offer for your big days. Stand to win a chance. Keep sharing posts and make your special day wonderful with us.
If you want to increase the number of visitors then invite your friends to like your page using invite option. Ask your collages to help for your promotion very kindly.