Assuming you have an airbrush? thats a BIG variable. If you do:
Pre-shade- use a darker color than the base color. Tamiya OD is really dark, so i usually use flat black. make sure you get the black over the ENTIRE model- especially in the cracks and crooks.
Base coat- Need a bit of airbrush control for this. load your airbrush with tamiya OD and paint panel by panel. However, leave black 1-2 cm around the edges of each panel (where possible). When you are done it will look kinda wierd, but we arent done.
high-light- Take some tamiya OD and add about 25% white, buff, or dark yellow (whichever you have) Then spray subtly in the centers in panels. Do this in verticle steaks on vertical surfaces and "little clouds" on horizontal surfaces.
Finishing touch- Now, what you have at this stage is a goody looking AFV. Dont fret, this is the easy part. (hard part was getting the flat black in all those crannies

.) Take some tamiya OD and thin it 50-50 with thinner. now spray in light passes over your model. It will take a couple of passses, but eventually you will see all the colors blend subtly adding more interest to your paint. As always, practice is key here. it takes a few tries to get it "right"
Now as far as how accurate tamiya OD is, well, its close enough. I personally prefer the Lifecolor shade but.......
Now if you are using a brush.....i dont have the slightest clue. Never was very good with those primative things.