What is the most common fault with the Toyota Surf motor blowing white smoke and hard to start?

If its a diesel it will be a glowplug or glowplug relay fault, should have 12volts at the bus bar and check each plug with the bus bar removed for continuity, open circuit means that glowplug is kaput. Also check by using a squirt of easy start, if it fires up without a fuss then it is indeed your cold start glowplug system and not something more serious like low compression/injector/pump problems.