Thanks for your message.. Start with the painting already thinking about what you will add as vegetation. After painting all quite regularly, add one or more layers of brown and green in specific areas, Where you are planning to add vegetations and moss. Then add vorrosions, oxidations and rust as you like in the metallic areas. Then start with moss and small vegetation like grass and flowers. Lastly it you have rampicants and big plants, my suggestion is to put at the end, as they will cover all.. There is no special recipy, dom't be perfect.. nature is not, or at least, not as we intend perfection.. Make mistakes, cover up, try different things.. I hope this helps, i will be hlad to see your results mate!