Hi @Smart Solutions.
It's tricky to give generic best practice recommendations without knowing a lot of detail about what you are doing or have already done.
There are a few things I can think of off the top of my head.
Ensure you're using HDFS Data Encryption for especially sensitive locations (though you needn't apply it everywhere).
Start looking at things like the refresh rate of your Ranger policies, ensure that's in-line with your expectations, setting the refresh time too low could impact the performance of the Ranger admin so bear that in mind.
Make sure that you're actually looking at the logging and auditing that Ranger is creating.
Start thinking about how Atlas could start to play a part in your security story, with things like the upcoming tag based policy control, Ranger + Atlas will be a very powerful combination. For more info take a look at: http://hortonworks.com/hadoop-tutorial/tag-based-policies-atlas-ranger/
Standard practices apply, ensure that people have the least permissions they need (both in terms of access to data and services) to complete their job, no more, no less.
Hope that helps, the fact that you already have Kerberos, Ranger and Knox in place suggests you're already along the right path.
Good luck and hope that helps.
