I put the keywords in my app's keyword metadata section. My app shows up at about #18 for the given key phrase (it's a two-word "key word").
My main concern is that people don't know what my app is about due to it not being explained in the name. However, it is quite popular, so I am conflicted about losing the simple branding in favour of a more SEO-heavy name.
That said: I have added a tagline to the upcoming update and will see if that effects discovery.