Few tips -
It's strange how you can get peoples eyes to deceive them.
For instance-
On a bomb or rocket....Paint it overall a single colour with not much else it looks 'flat'.
However add some lower shading and upper highlights it looks a lot more round.
Same goes for the main fuselage for the most part.
Wings, tail, and tailplanes - A very slight darkening around the edges with a highlight running parallel to the leading edge gives them more depth also.
Experiment! Use different blend modes on the layers (lighten, darken, soft light to name a few).
For dirt and weathering use pictures of the real thing to see where and how it happens.
A blob of colour then using the smear tool will give good oil streaks.
Here is one I did for another game, it uses everything (plus a bit more) that I explained above.
Good example is the apparent gap between the engine cowlings and the exhaust, it isn't there. Just 'painted' on to give the illusion.
The ailerons, elevators and rudder are given a solid outer edge and a slight blur on the inner edges. Finally finished off with a highlight on the front edges, just behind the faded dark edge.
Helps to make the leading edges look round. -
