You can find detailed information about how to get to the Stanmore Campus on the Royal National Orthopaedic Hospital website. There is also a Stanmore Campus map.
If the weather is fine and you are able to, there is a pleasant, but hilly walk through the park from the station.
Also, the Wood Lane entrance (opposite the entrance to the Aspire Leisure centre and next to the Cloisters development) offers a handy cut-through to Stanmore tube station, via Kerry Avenue. Be warned though, once you leave the all weather path, it can get very squelchy and muddy if it's been raining - we recommend you wear some decent waterproof boots or trainers, unless it's the height of summer!