In most FF programs, there must be some activity within X(usually 3) years to keep miles from expiring.

1. Donate a minimum number of miles to a charity.

2. transfer a minimum amount of miles into the account. Diners has a large number of transfer airlines. 95 point charge for 1000 miles transfer.

Starwood AMEX has a large number of transfer airlines, with no charge but minimum transfer. 20,000 starwood points transfer to 25,000 miles at participating airlines.