For Wishes, stand in the middle of Main Street right by the ice cream parlor. You will have the perfect view. It depends on how busy the park is. If you have spectro right before the fireworks, I would just hang out and wait. If not, I normally go about 10-15 minutes before.
For Illuminations, it depends on the breeze. Before it starts, look at the flames to see which way the wind is blowing. Go on the opposite side of the lagoon as to where it is blowing! and that one, I don't camp out for. Maybe 10 minutes or so.
You can see the fireworks no matter where you are standing. so if you want to fit in something, go do that first and then go. It isn't really worth camping out for a half hour or whatever. You can always see over someone (they are in the sky!)