Theuns: Doogs found this technique and had great success so I 'borrowed' it from him.
1). Undercoat of gloss black
2). Alclad airframe aluminum
3). Post-shade (paint centers of panels) with plain aluminum
4). Light misting of aluminum overall to dampen the contrast
The airframe aluminum is more shiny and slightly translucent showing the black though slightly so it's a little darker. The plain aluminum in the centers is lighter giving a pre-shade effect.
You can also just as said paint the different panels black or grey and then spray everything plain aluminum and you'll get slightly different panels. There's a lot of different things you can do with it, I find the Alclad very easy to use- it's getting a good smooth perfect undercoat that's the problem for me.
I've been sealing the model with Model Master Metalizer Sealer but here lately I've noticed the NM looks kinda dull and off so I may stop using it. You don't have to cover the Alclad with anything. I will spray a little matte varnish on the decals if they're shiny, not sure if they need protection though.
Don't spray the whole model with matte varnish though- it makes the Alclad turn really dull and look like cheap silver paint. I found out the hard way!!!