Aeons ago I was advised by pro painter in the US that if the surface is already painted with a strong colour, to undercoat first with a medium to light grey; as this effectively blocks any tendency of that strong coloured to in effect bleed through (show through as it it were) if the intended colour(s) are on the light sider. More applicable usually to indoor redecoration but equally applies to exterior.
Also if wanting a really smooth finish when using gloss, sand down with a light/fine grit between all primer/undercoats coats, or in some situations a fine wet ‘n dry; and don’t forget to go over with a sticky rag after vacuuming the surface(s) and surrounding areas each time. Equally for so satin/matt finishes too. Same applies if using gloss urethane “varnishes” etc. finishes.
Nothing will irritate more if there are nits and bumps on a nicely gloss painted and highly visible surface; especially a front door.