Lunges?

Try building up the stability around your ankle, knee and hip joints first. Good way to do that is simple balance exercises and techniques (Single leg balance, single leg balance w/ eyes closed, single leg balance with rotation etc.). Also try single leg squats (keeping hips square and back in neutral) and body weight squats. Be sure not to let the knees slip inward or out of alignment of your second toe. Lunges take some flexibility and stability in order to perform them with proper technique. Most people lack the flexibility for a full lunge and lose neutral back on the way down (round back or hyperextend in order to compensate for lack of hip flexibility). Make sure you keep your back in neutral posture while doing ALL strength training exercises.

If you lack flexibility in the hips be sure to use a dynamic stretching routine or foam roll before your workout and static stretching routine after. Static stretching shuts down CNS, which is not what we want before a strength training routine.