Documents
Airworthiness Certificate
Ensure it is in the aircraft
Verify the tail number on the certificate matches the tail number of the helicopter
Registration
Ensure it is in the aircraft
Verify the tail number of the registration matches tail number of the helicopter
Check expiration date (typically valid for 7 years)
Operating Handbook
Ensure it is in the aircraft
Verify the tail number for the POH matches the tail number of the helicopter
Weight and Balance
Ensure it is in the POH
Ensure that any changes to the weight/balance of that aircraft are documented
Hobbs
Verify starting time on meter (recommended to take a picture of it)
Squawks
Located in the aircraft binder
Be aware of any recent issues
Look for any trends that could become a likely problem for your flight