Squats are an absolute must. But like fitfreak said make sure your form is correct. Also, yes full range of motion squats are important but if you can't get down there without clean form then work with in your given flexibility level and try to stretch your soleus and hamstring muscles so that you will be able to do complete squats. Also, don;t up the amount of lower body training you do in a week, this will lead to overtraining and possibly atrophy.
peace.