This is a great article posted on another site (who reposted it from another site, who took it from another), but I thought many would enjoy it here. It is The Lazy Man’s Guide for Constructing a Call of the Cthulhu Adventure, written by Sandy Petersen, original author of the Call of Cthulhu.
In Azur, the streets are crowded, and the PCs' poor grasp of Azuran makes it hard for them to find out why. Still, they shoulder their way through the crowds, trying to get to the house of the renowned wizard they seek, when suddenly they realise they are standing very much alone. The crowds have ceased their talking and their gazes are fixed on the PCs. The imperiously clothed man standing before them smiles and speaks in Azuran: "Ah! Volunteers! And so eager too!"