All parts should be lubricated with a good quality, clean lubricant prior to replacing.
Install the seals onto the piston.
Insert the piston and piston rod into the barrel.
Install the seals into the head.
Carefully slide the head onto the piston rod butting it up to the barrel evenly.
Install and tighten the tie rod nuts.
Install the clevis (and jam nut if one is used) and tighten on the piston rod.
Plug the ports on the cylinder and re-install on the equipment. Remove the plugs and connect the air lines.