The one thing I like to point out is that weathering is 90% observation and 10% technique. There are lots of ways to get to the results. Do a little reading and see what people do. I use a lot of acrylic paint and mixing of colors to achieve results. But that is not the only way to skin the puppy. You can use the powders, you can use pastels, you can use India ink, you can use an air brush you, can invent your own ways.
The key is seeing what is there, deciding what is significant enough to model, then formulating a plan to achieve the results.