My favourite board game is Cluedo (or Clue in the USA).
To begin the activity I usually turn all the lights out in my classroom and have the board already set up. I often will play some scary haunted house music which I use at Halloween, to set the scene.
The students come and sit round the board and I explain that we are no longer in a classroom, but in an old house; the house of Mr Black. I ask the students to look at the board and say what rooms they can see. Students then ask what the Ballroom is and so on, eliciting vocabulary along the way and beginning with a discussion about the different rooms.
Next I introduce each of the characters eliciting basic colours before moving on to tell them each of the character names, explaining the synonyms of Scarlet, Mustard and Plum. We then look at the different character titles such as Professor, Colonel and Reverend and I ask each of the students to tell me what they think each characters' job might be. For Reverend some students often say "he works at a church" and I reply with "yes, we call that person a priest or a vicar".
Leading on from here I finally introduce the murder weapons, eliciting the different objects. When the students see the revolver they often will say "It's a gun"; for this I will then tell them, "yes, but we can also call this a revolver" introducing new vocabulary along the way.
Finally I explain how the game works to the students and write on the board the words "I think it was...." this is a good way to revise past tense, along with prepositions e.g. "with the..." and "in the....."
Usually during the first game I take it very slow with the students, but by the second and third game the students become more confident and enjoy playing the game. Later, when writing short stories I discovered my students were using some of the characters and rooms of the house in their writing. Overall a fun learning experience and a great game to get the students problem solving and speaking.