To encourage rail use, it should be easy for passengers to get to the train station. Provision of secure, well lit and CCTV covered bike parking should be a priority, along with local bus services timed to connect with arrivals and departures.
However, provision of parking helps as while trains are good at getting large numbers of people into cities, they're not great at stopping next to everyone's house. There are essentially 3 classes of station I can see.
1: Rural/suburban/small town stations where a free car park is provided, but not used by non-rail users or overcrowded to a level that makes charging necessary.
2: Major City Centre Stations, where no car parking, or limited expensive parking is provided in line with local non railway rates. e.g. London Terminals, Edinburgh, Manchester.
3: Intermediate sized towns which are commuter and/or intercity railheads but also limited commercial and shopping centres in their own right. These stations should have car parks with a charge, but some or all of the cost should be refundable against a train ticket to discourage non-rail users. Examples might be Milton Keynes/Falkirk for commuters, or Warrington/Doncaster for Intercity.