I reduced one series to 99 cents for all thirteen books, and made sure that each week a couple of books were available for Kindle Unlimited. Not very strategic, and I didn't want to appear to be in any way taking advantage of people who were hurting.
I sent a few paperbacks to nursing homes, and then stopped because some didn't want to bring in outside items. I'm going to try that again now that it seems COVID-19 is not generally spread through contact with inanimate items.
My broad suggestion for sales during a time of crisis is the standard one -- consistency. I've expanded my number of tweets and continued to update my webpages. Here are a couple of other things I'm doing. I can't vouch for their effectiveness, but they make sense to me.
1) Reexamine your book categories by studying those of similar books that sell well, or books that address similar topics. For example, I looked at how Amazon categorized The Twain Does Meet and saw two categories addressed culinary mysteries.(The book does mention that Jolie is not a very good cook, but there are no recipes.)