What to do when the keywords are dropping? - I have discovered that the week-over-week traffic dropped by 40%. Where do I even begin looking to fix this problem as soon as possible?

I have keywords that were doing the Google dance, but now they are dropping in rankings. When I open up a keyword tracker tool, I see a lot of the keywords with the RED arrows and pointing down.

What should I do to get the keywords in green to present a keyword report to the client?

The drop is not only today, it has been for the past couple of weeks. So I don't know if I should rewrite the content for those keywords that are dropping. What is the proper method to get them up again?

I have discovered that the week-over-week traffic dropped by 40%. Where do I even begin looking to fix this problem as soon as possible?