Lets see if I remember the sequence properly..
First, start by giving them a good wash(i.e. lather-rinse etc.). The vinyl has gunk on it that helps release it from the mold. When thats done you can go two ways. Lightly weathered or muddy. It depends on the situation you want your tank in. If the tank is lightly weathered, paint them gunmetal, then a drybrush rust colour, then drybrush lightly with silver, or use pencil lead.
If you want the really muddy stuf, like on the Panzer IV in my pic below, paint the tracks whatever earth tone you want, then drybrush with gun metal then again silver or pencil lead. you can also give them a bit of a nicely diluted dark wash, just to bring out the details, but its not really neccessary.
You'll find that every armour modeller will have a different method. (though to be truthful, I'm quoting the first method from what Robert, aka Shermafreak, said to someone a while back)..