Low Poly Struggles (I'm flummoxed)

So I’m modelling this little low poly creature to get the hang of… well, everything. I’m planning to texture and rig him, the whole 9 yards. I’m doing alright so far (I think?), it’s all quads.
I just have no idea how to approach the mouth. I want it to be nice and round, so I’m definitely going to have to add more faces but I’m just really stuck on how to get the shape I want (I should have drawn him with a neutral expression, because that’s how I want to model him -_-).
And then from the mouth I’m going to have to figure out the eyes and tbh I’m completely flummoxed with how to approach this.
And tips/advice would help immensely.

Select faces and inset them (shortcut I). Look in toolshelf or F6 for additional options

Or just use a texture