Consciously squeeze your glutes hard while doing your exercises Clench your glutes as hard as you can.
When you do a lunge, squeeze the glute hard while you're pushing up. This will help to activate the glute muscle. It's all about getting your mind into the muscle and forcing it to contract rather than just going through the motions of an exercise.
By concentrating on squeezing the glutes hard during your sets (of whatever exercise you're doing), you'll be activating the muscle fibers of the glutes and increasing the amount of work they do.
If you don't believe this technique can work, try this: go for a walk up and down some hills squeezing your glutes hard as you push yourself forward with each step you take.
Push with your heels
The transmission of force and tension from your foot through your leg and glute can be altered by where you put the tension on your foot. If you push with the balls of your feet (the forefoot area), more tension will be placed on the frontal thigh (the quadriceps). If you focus on pushing more with your heels, more tension will go through the back of the thighs and to your glutes.
By pushing with your heels, you can take advantage of this force/tension relationship. For example, when you're doing lunges, try to raise the toes of your front foot off the ground. This removes tension from the front and focuses more on the heel. This will, in turn, send more tension to the glutes, making them work harder.
There are several practical techniques you can use to really force the heel push.
If you're doing the leg press, you can focus on the glutes by placing your heels on the top edge of the foot plate. When doing squats, simply raise your toes up in your shoes to achieve a similar effect.
Visualize "sitting back" when you're doing your glute exercises.
This idea is similar to the concept of pushing with your heels above. When you "sit back," more tension will be sent through the back of the thighs and the glutes. If you lean forward , you will tend to throw more tension on the quadriceps.