Generally speaking, eyes tend to be an equal distance apart, with about one eye’s distance in between. Again, this is in terms of realistic proportions—stylistic works may exaggerate these proportions.
Keep in mind, however, that “breaking the rules” can have mixed results! For example, larger eyes might turn out visually appealing, but eyes that don’t have a strong, visual relationship to each other could come off as unusual or visually awkward (unless that’s what you’re going for!).