So use dialogues rather than lectures. Ask lots of questions and have them write as well as speak the answers. And get them involved in designing the training. Ask them how they would like to learn. Show them that the learning is useful.
Adults expect their learning to be practical and relevant.
And they will best retain what they immediately put to use. So as soon as you've trained them, have them put their training to work. Reinforce the learning. People remember what is reinforced. That means you need to tell them frequently what they're doing well.