Molina: I don't know if is your first model, but welcome to the world of modeling, my way to do it is first asembly the whole model including the accesories and then primer the model on a primer gray or rust color depends on you, then paint the scheme, for ambush i sugest to look at real pictures of tanks or models in the internet and always start painting the dark color then the rest, the last thing i do is the tracks, if they are from plastic or piece by piece assy, all and then painted in rust (testors 1185 is good) then let them dry for a day, next given them a wash(heavy wash) with black (80% tamiya Thinner, 20% Black Paint), let them dry for one day and the last and best step, grab a pencil and with your exacto knife peel all the grafhite and use your finger to aply to the track.
For weathering on your model use drybrush techniques or powders.....good luck and if you have a question feel free to ask me.....
Gabriel Salazar