The first technique is from Alastair Brotchie's collection of surrealist games. The second is a variation on the first. Like all such games, it is important to play them freely, without concern about "making a good one" or being clever. If the players feel free, the results can sometimes be remarkable. We are used to trying to work together rationally, these games ask us to work together irrationally, creatively.
In pairs or a group: each person writes the first clause of a sentence, beginning with "If", on this pattern: