Formal:
* J'aimerais jouer au Scrabble. (This is the most common and neutral way to say it.)
Informal:
* J'ai envie de jouer au Scrabble. (This means "I feel like playing Scrabble" and is more casual.)
* J'aimerais bien jouer au Scrabble. (This is similar to the formal option but slightly less formal.)
* On pourrait jouer au Scrabble? (This means "Could we play Scrabble?" and implies a suggestion.)
You can choose the most appropriate phrase based on your relationship with the person you're talking to.