You also have the ability to "nudge" an object using the arrow keys, which may give you more control than the mouse but less trial-and-error than using the numeric fields. Check somewhere around pg 148 in the manual (or just use the text search feature in the Adobe Reader to find nudge): "Press and hold the Command/Ctrl key, and then press the arrow keys to move the object in the active plane." You can also use the shift key to get smaller increments.