I like the basic shade of light gray all over, but then there are dark lines where there are panels on the fighter. If there were grooves in these locations I would say just using a pencil to show the panels.
However there are no grooves to run the pencil down.
Whilst i can’t profess to know the exact answer, my suggestion would be to pre-shade those lines with a darker colour (how dark depends on the overall colour, eg, a dark gray under a lighter shade of gray), the same way you might pre-shade panel lines prior to painting.
Then paint over the top (you should be able to see a very faint outline of the pre-shade underneath).
Following that, and depending on whether you think they contrast enough, use some ground pastels on a brush and go over those pre-shaded lines, to make them pop a little more.
Hope this helps.
I’ll be interested to see anyone else’s tips too - perhaps I can refine my technique or even learn a new one.