The number of keywords that you should use for ASO (App Store Optimization) will depend on the specific requirements of the app store you are optimizing for and the length of your app’s title and description. Here are some general guidelines to keep in mind:

1. Google Play Store: The Google Play Store allows you to use up to 5,000 characters in your app’s title and description, so you have plenty of space to include a wide range of keywords. However, it’s important to strike a balance between using enough keywords to attract users and using too many keywords that might make your app title and description seem spammy or irrelevant.
2. Apple App Store: The Apple App Store has stricter guidelines for app titles and descriptions. The app title can only be up to 30 characters long, and the app description can only be up to 4,000 characters long. As a result, you will need to be more selective about the keywords that you use. It’s generally a good idea to focus on your most important keywords and use them in the app title and the first few lines of the app description.
3. Amazon Appstore: The Amazon Appstore has similar guidelines to the Apple Appstore. The app title can only be up to 50 characters long, and the app description can only be up to 2,000 characters long. As with the Apple Appstore, it’s important to be selective about the keywords that you use and to focus on your most important keywords.

In general, it’s a good idea to use a combination of short-tail and long-tail keywords in your app title and description. Short-tail keywords are general terms that are commonly searched for, while long-tail keywords are more specific and less competitive. Using a mix of both types of keywords can help you rank for a wider range of search terms and attract more targeted traffic.