For example, on my Elemental King I painted his collar and metal plates a cool blue-grey NMM steel but then used iron RMM to create layers and sheets of rust. On my Harlequin Wraithlord, I used a little bit of NMM to highlight some of the TMM gold in order to force a visible highlight not dependent on the strength or angle of actual light reflecting off the paint.
I'll show you some examples and offer some tips on ways you could use this.
Recently, on the mounted leader from Age of Sigmar, I used metallics to create a shiny undertone that blended into natural set highlights. This was actually done in only 4 steps - Metallic gold primer, a thick brown wash, then an off-white highlight followed by quick white highlight of tips and corners.