I am sure Robo will be along to show you his incredibly helpful maps. Anywhere in the street around Caseys/Plaza up toward the Frienship statue is great. You don't want to get too close to the castle or you will have a partially obstructed view.
We grab a spot on the curb about 30 min before MSEP, near a crossing sidewalk. Sitting on the curb will prevent anyone from sneaking in front of you for the parade. Then, about 15' before CTM or Wishes, the CMs place masking tape across Main Street to designate areas to preserve for pedestrian traffic. If you toe that line, you will have a gap (the imaginary sidewalk extended into the street) in front of you where no one can stand. That gap is a nice buffer zone between you and anyone else, protecting your view and giving you some open air space.