One common prophylactic idea is the advance of the rook pawn near a castled king, which can be done to provide luft and/or to prevent a pin; another is to transfer one's king to the b-file after castling queenside so as to protect an unmoved a-pawn, among other purposes.
Prophylaxis is a distinctive feature of positional play, often preventing opponents from entering risky, double-edged lines, as well as punishing opponents who play too aggressively.
Famous practitioners of prophylactic play include Aron Nimzowitsch, Tigran Petrosian, and Anatoly Karpov; even tactical players, such as Mikhail Tal and Garry Kasparov, make use of prophylaxis.
[1] The term prophylaxis comes from the Greek προφύλαξις, profýlaxis, "guarding or preventing beforehand".
The diagram shows a common opening known as the Sicilian Defense, Najdorf Variation, arising after the moves 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6.