There are as many ways to do it, as there are artists who do it!
Personally, I start with a very dark grey, almost black, covering everything.
Like so...
Then, I'll "marble" on some white, mainly within the panels, like so...
Then the color. This is thinned down at least 50/50, if not more. Just light coats to slowly build up the color. Stop when you have the coverage you desire!
I find this technique is great for modern, grey/grey jets. Them suckers get all kinds of dirty and varied in their paint.
Here's a few examples.
With this F-14, I did go back over some areas/panels with a very thin and lightened mix of the base color.
Before the clear coats...