Are you working out at home or at a gym? My gym routine includes squats, lunges, presses, extensions & ham curls as heavy as I can. Squats, lunges & presses can add some size. Extensions & ham curls target your quads & hams more specifically & will help add definition.
However, much of this depends on your build as well. I'm really petite & even though I can get well defined it's very difficult for me to add size.