That already looks to have a lot of decoupling caps so maybe the issue is something else.
Depending on where you are feeding the VIN to the Arduino you may want to add some extra filtering on the regulator.
Maybe also increase it to between 7-10 volts too (again depending where you are feeding the VIN)
You seem to have the 7805 in the most basic configuration.
The LED also has a secondary purpose in the pic above in adding some protection too.
A lot of other schems will show a 1n4007 or similar in place of the LED and resistor.