faces not dividing properly

I’m trying to create a simple model, but I find as I go that the program designates arbitrary faces as not being able to subdivide, meaning that as I come to sculpt those areas into curves, I find myself unable to. is there any way of fixing this, or at least of avoiding it coming up in later models?

You probably have ngons (faces with more than 4 vertices) there. When you subdivide an ngon, you get an ngon.