The most common changes are for bigger or smaller riders who want a wider or narrower handlebar. If your handlebar put your hands significantly more or less than shoulder width, consider changing your bar. If the bar is too large, you can even cut it down yourself. As far as adjusting your bar, it can be rotated by loosening the clamp that holds it in the stem. That is, the sweep should not be pointing up or down, but directly rearward on a horizontal plane.
Grips are very easily and inexpensively changed.
Once again, personal preference is the key. Some people like big, fat, padded grips, while others like a thinner, more direct connection to the handlebar. See your dealer if you think you'd like a different handlebar or set of grips. Most stems have some sort of height adjustability, and also come in many different heights, lengths and rises. Combined with the handlebars, you can dramatically change the feel of the control center of your bike by utilizing the adjustment features your stem.