What are your shooting conditions? Can you post a typical image you are unhappy with?
With the camera set to Standard Picture Style in Auto mode you should be getting sharp colorful images.
In limited conditions, where you might be getting reflections from water or off leaves, a polarizing filter might help. But these are very limited conditions.
While I don't know the ladies in the image to know how accurate it is, personally I think it is a fine photo.
I see from the EXIF you used the Portrait Picture Style. The Portrait PS reduces the camera base sharpness setting to provide a smoother look to skin. It would be more suited for head shots where the subject's face is a large part of the image. For the setting you have you might try Standard as well as possibly fine tuning the Picture Style as kvbarkley showed.
Filters do not improve image quality. There are many who argue that filters degrade image quality. Filters can be used to make some type of desirable change to your shooting conditions.