This question is not easily answered, as there are a wide range of contributing factors.
I would personally recommend running a report for event counts by signature ID, and just start going through your top 10-15, and slowly start adding signature IDs that are needed to a NOT filter, and re-generating the report until you have cleaned up rules that are of no interest to your company.
This would be the approach I would take.
KB84679 mentions some events that seem "extra" and unneeded. I have been following Ryan's advice, and agree with it, but sometimes you need to look at your internal processes. For instance, filtering events caused by Altiris or Bigfix or Tanium (whatever you use for patch management) might remove a bunch from your environment.