If they've been through an academy then in the gear. If not then start in a dark area of the firehouse. Couple simple runs and then as they develop work up to blacked out mask on air with hazards. Simple drills on runs are good too. "Left or right search?", "How would you continue your search here?" etc... It has to be a habit. Muscle memory. Then I guess the end goal would be search and rescue drill with a dummy, notification and removal.
Just my 2 cents. I've got a couple more if you want them.