Forward lunges are similar to step back lunges in that you start standing with your feet side by side and end up in the same bottom position. The difference is you step forwards instead of backwards from the starting position.
This small change may not seem like much, but it has a significant effect on how the exercise is performed. Specifically, this variation requires a greater level of both muscular power and control.
To start the exercise step forward and have your heel touch the ground first and then the rest of your foot follows. At the same time, you will be bending both knees, so you end up at the bottom position with your front knee directly over your front ankle. This all happens in one fluid motion, so you need to step far enough to allow all your joints to bend without restrictions.
Once your front heel touches the ground, the movement changes from being more of a forward motion to a straight down motion. Otherwise, you will likely either end up with your front knee going too far forward or your upper body will bend forward. As with other lunges, you still want to maintain good posture with your upper body and stay as upright as possible.
Returning to the starting position is also different from a step back lunge and is the most difficult part of the exercise. Instead of just stepping back to the starting position, the goal is to push off with your front leg with enough power that you get back to the starting position. The temptation will be to pull yourself up using your back leg, but you want to make the front leg do as much of the work as possible.
One of the signs that you are doing the exercise correctly is having a minimal amount of noise, especially when landing with your front foot. If your foot contacts are hard/loud it means the stabilizers need to develop better strength or control. If this happens, you can perform the exercise while holding on to something or having your hand on a wall to provide extra stability.
Perform up to 15 reps on each leg and breathe out when standing up from the bottom position. Stop if your form deteriorates, you are not able to land softly with your front foot, or you are not able to push yourself all the way back to the starting position with your front leg.