For either player, get a center pawn duo: e4 and d4 if it's an e4-opening, d4 and c4 if it's a d-pawn opening. If one of those center pawns gets traded off, then still bring out the other as you would have if you'd had both (e.g., 1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. d4).
