To find the correct torque specification, you must consult a factory service manual for your specific Ford Focus 1.8L engine. This manual will provide the exact tightening sequence and torque values. Using the incorrect torque can lead to a blown head gasket or other serious engine damage.
You can often find these manuals online (some are free, others are paid) or purchase one from a parts store or online retailer. Be sure to specify the exact year, model, and engine code of your Focus when searching for the manual.