In the past, the final stage of painting a model has been highlighting. It is a step that has necessarily come after all other layers are done. In the past, I have gotten out my finest detail brush and slowly put thin lines on the edges of my minis. It has worked with varying degrees of success.
Sometimes my highlighting has been good, like the stormraven (which I didn't actually finish highlighting) with nice thin lines. It helps that the model has lots of edges. The Deathwatch Space Wolf I consider decent, where the lines are clean, but thick, which doesn't really have the same enhancing effect I see with professional highlights but rather stands out on its own. Sometimes the lines are so thick that on the Kastelan I didn't even highlight all the edges as otherwise the highlight color would almost completely obscure the true color layer underneath.
With the Alpha Legion, I am trying something different.