Or on a F70/F100, reverse thrust selection is blocked until both mains are on the ground. When permitted, reverse thrust is inititated by firstly selecting idle thrust (where the thrust levers should already be) and then by lifting the "reversers" on the thrust levers. This action will manually deploy the lift dumpers, if not automatically deployed, and then give you idle reverse. Pulling the "reversers" will increase the reverse thrust until you reach "emergency" reverse.
PM