With armor I mostly build my major sub-assemblies (i.e. upper hull, lower hull & turret). I mount my smaller parts (pioneer tools, road wheels, headlight assembly, etc.) onto a piece of cardboard so I can do them all in one fell swoop.
I fill obvious gaps and such before painting then go back and fill any that are exposed by the primer.
Once I've got all my seams filled and everything is evenly primed then I'll go with a couple coats of my chosen base color.
The thing is, just about everyone here will have their own style and methodology. There's not right or wrong way to do it. Everyone has their way of doing it. Cherry pick whatever ideas you find here and formulate your own personal attack plan.
We can all learn from each other here.