Concrete has a tough time outdoors because of a combination of frost and deicing compounds. You should start by hammering and brushing off all the loose material. Then dampen the concrete. You don't want any standing water, which would dilute the new coatings, but if the concrete is too dry, it will draw the water out of the new material. For best adhesion, apply a bonding agent or primer made specifically for concrete. Simply paint it on. Be ready to work quickly, as you should apply the patch after the bonding agent gets tacky but before it gets dry. If your cement patch comes with a mention on the bag that it is "polymer modified," then simply mix with water and apply according to the instructions on the bag. If it is not polymer modified, use the bonding agent rather than water to mix the patch material. Do not water the patch with a hose as it will rinse off the polymers, rather cover it all with a plastic sheet to prevent evaporation. Leave it set for three days.