Tamiya weathering powders...tips/hints?

I accidentally posted this in “Tools” but figure it belonged here.

I bought a few of the sets based on the praise of other modelers here and the fact that they seemed loke a great idea. I’m planning on experimenting with them on my “crash test” model and thought I’d check in here for any suggestions ( especially since I don’t know Japanese, which make the enclosed directions pretty much useless ).

So, any suggestions or warnings I should be aware of?