A low cache hit ratio generally indicates that you need to parameterize queries to allow them to get reused.
You can increase the cache hit ratio by parameterizing queries in your code. You can use the Queries Needing Params report to find the queries that you can parameterize that will free up the most cache space.
If you don’t know what database to start with, use the Queries Needing Params By Database report to find the database taking up the most plan cache.
Once you find the queries that are the worst offenders, you can use the Queries Needing Params Advisor to figure out how to parameterize them.