Make the balsamic glaze first, so it has maximum time to cool. In a small sauce pan, mix the ½ cup balsamic vinegar and 1 tbsp honey well, and heat over medium until it is bubbling, about 2 minutes. Watch it carefully until it reduces by half and is thickened. Cool by pouring into a heat-safe dish and placing in the fridge.
Prepare the other ingredients. Slice the 6 cups watermelon and clean and prep the 1 pint blueberries. Crumble the 3 oz feta and clean and slice the 12 leaves basil.
If you are serving immediately, you can add it all together. If not, keep ingredients separate until ready to serve.