Today, part III of our series on pawn centres. Check out part I and part II. Once again, I draw on Bruce Pandolfini's Weapons of Chess. After the open and the closed centre, Pandolfini discusses the fixed centre, also known as blocked centre. It consists of two pawns blocking each other.
In fixed centres, you battle for control of the empty centre squares: aim your pieces at d5/f5 and d4/f4, respectively and secure them as outposts for further advances. Place pieces on outposts for an attack or to provoke a pawn move that messes with your opponent's pawn structure. Rooks can protect your outposts from the open file. Knights on c3/c6 defend the centre pawns and occupy an outpost square once secured. Defending pawns with bishops should be avoided because the pawns reduce the bishops' mobility along the diagonal; use your bishops to protect an outpost square instead.
Don't push your c-pawns to c4/c5 unless you know what you're doing: usually, these pawns are needed to chase away your opponents' pieces from their outposts, and pushing them weakens control of your own territory tremendously. Attacking players may be tempted to use the f-pawn for a pawn break, but this is much more dangerous in a fixed centre than a close one because of the open d-file; if your opponent attempts such a pawn break, remember the dictum "When attacked on the flank, strike back in the centre!".
I'll try to find an illustrative game as soon as I have access to my chess library again.