If you don't have a small-loop resistance band (aka a miniband), you can do this glute activation exercise with just your bodyweight. Either way, don't step your feet completely together as you walk; keep them slightly apart so your glute muscles remain engaged.
Place a resistance band just above or below your knees (the lower it is, the harder it will be). Begin standing with your feet directly underneath your hips, and squat about halfway down.
Engage your core, and take a large step sideways to the right.
Actively resist the pull of the exercise band as you bring your left leg slowly toward your right, returning to the starting position.
That's one rep. (Be sure to do an equal number of reps in both directions.)