Check the train schedule on the National Rail website.
Go to London St Pancras station. St Pancras is located on Euston Road next to Kings Cross station. If you're taking the tube, Kings Cross is on the Northern, Victoria, Piccadilly, Metropolitan, Circle and Hammersmith and City lines.
Take the direct train from St Pancras Domestic station to Luton Airport Parkway station.
Board a shuttle bus to reach the airport.