This is a tip off the Power and Bulk forum by Lyle McDonald. Very simple, very elegant.
1. Stretch hip flexors (tight hip flexors inhibit the glutes)
2. Lie on the floor, feet about shoulder width, with a lifting belt just above your knees.
3. Push your knees out into the belt. This activates the hips external rotators.(inc. gluteus medius/minimus)
4. Set your abs and low back tight
5. Bridge up into hip extension by pushing through your heels.
6. Hold at the top briefly.
7. Do as many reps as needed until you feel the glutes really firing. This may be 10-20 or less or more.
8. IMO, I think moving straight into a light set of compound work (squat, dl, front squat) helps to integrate the recruitment into the more complex movement.

You can do glute bridges as part of every warmup and in-between sets of compound lower body work to make sure they keep firing. Keep stretching your hip flexors too.

Lyle’s web page is HERE