Short and sweet - 4 tips on keywords that will help you make the right choices:

  1. Never make automatic translation to keywords - You need to find the right keywords in every language you publish your app in.
  2. Find keywords in user reviews - the best source for finding the most relevant keywords for your app.
  3. Understand the Appstore algorith better - positive reviews and higher user rankings make the best rank for each keyword, when mltiple apps are using the same keywords. If the keywords appears in the app name itself, that also has a lot of value.
  4. In-App Purchase keywords - your IAP name, if searched in the **exact **phrase, will also influence where you will appear. So make your IAP name easy and 'catchy'. And put them in your list of keywords.

Full article here:
http://www.appmasters.co/aso-app-keywords-4-facts-to-increase-exposure/