Isn't what you doing called a pin wash? You might look up 'color modulation' too. I'm no expert but there's several around here who are. 

OK.......... 

                                       
                
    Here's all 'ya need.

(well that isn't going to work, I just LOVE this new forum format)

If you wnat to highlight the raised parts, try a dry brush with a lighter shade of your base coat followed by pin washing.

Bocks Suv

Building a 1/35 Merkava and just ABed it a typical dark military green, but now it looks flat and kinda boring. I'm tempted to highlight the raised parts, fiddly sections and seams with a very thin black paint, but wondering if that might get lost too and instead should I go with a lighter highlight color? Any tips would be appreciated.

 

Two techniques here, you will need an airbrush for implementation:

First is preshading to realize depth and contrast on OD green:

First, fill all seams and create welds with putty:

Next, an overall coat of dark gray / black:

Overspray with OD green and some polyscale flat mixed in:

Finally, fuel / oil stains applied with extremely thin gray / black, and, a lighter shade of OD across the top of the model (as the sun would hit it)

Finished product, with accents ..brushed on MiG pigments: