Try applying a wash to all the nooks and crannies , I use Burnt Umber
watercolour, mixed with a little black, with water and dish soap to
help it flow properly. Any excess can be wiped off with a damp Q-tip
after it has dried.
Then you might want to try a little dry brushing, using a lightenend
blend of the base colour, don't use white, as the effect is too stark.
Just load up a flat brush, wipe it clean, then give it a scrup across a
piece of card or paper to ensure that you don't get any blobs, and
gently brush it back and forth over the raised details of the model.
You can also panel shade, by spraying a dilute mix of black/dark brown,
mixed about 10% paint to 90% thinner along panel lines etc. Just do it
enough so that it is barely perceptible, it adds a little depth to the
finnish.
Finally you can apply a 'Filter' coat over the entire model. This again
is a very dilute mix, using a pale colour, such as buff or sand,
sprayed from a distance of about 18 inches over the entire model. This
helps pull all the wearhering effects together, while knocking the
colours back for a more scale effect.
Hope this helps.
Karl