Build steps

Everyone has there own approach. Mine is to assemble everything that is the main colour/colours and then paint. For a tank i keep the turret and hull seperate. I tend to leave the wheels off as well.

You will need to use a gloss coat for decals, but many armoured vehicles only have a few. You could just apply spots of gloss where the decals are.

My best suggestion is to check out some of the armour builds here and you will see a number of ways of doing things.

For AFV, I am much the same as Bish, build up as much that is the same color.  Keep turret, wheels, tracks and hull seperate.  I tend to also glue on all the small bits, like tools, tow cables, sand bags etc.  I will go back and with a fine brush paint these right on the model.

As Bish already mentioned. Keep in mind, there's no set rule on how you do your build, let alone when and what to paint first, last or whatever. In time, you will get the idea what works for you.