Assuming the glow plugs are working ok, if not see checking glow plugs
Common rail diesels can suffer with worn injectors typical problems would be poor starting (long cranking times) and low rough idle practically when hot. The problem with the injectors is not bad spray pattern but excessive leak back, the injectors when new are designed to allow a small amount of diesel to leak back through the injector to remove any air bubbles and keep the system bleed. If this leak back becomes excessive due to worn diesel injectors the high pressure diesel injection pump cannot produce sufficient pressure to overcome the leak back at low rpm this can give poor starting and/or bad tick over. May start with Easy-Start, due to engine turning faster.
Diesel injectors can easily be tested for this problem by attaching small bottles to the leak back pipes, the manufacturer will give a leak back figure in cc but a worn injector will fill the bottle in 20-30 seconds as opposed to a dribble from a good diesel injector.
If leak back is normal the rail pressure would need to be checked older systems producing 1000-1350bars and newer systems reaching 1300-1600 bars which can be tested with electronic test equipment.