I wouldn’t wear a princess dress every day in the park. You should wear it on days at EPCOT or Magic Kingdom because you can meet princesses there and wear it in the pictures.
The dresses are hard to keep clean in the park. If you have a dress, pick it up and make sure it doesn’t drop on the ground. In my Jasmine costime, scoot the pants up. If the sidewalks are yucky, Pack a shout wipe (or 5).
Sandals or flip flops look best with the dresses. Tennis shoes look stupid. Just don’t do it. If the sandals are uncomfortable on them, you shouldn’t have bought them in the first place.
Try on your princess dress before going to the parks to make sure it isn’t itchy. Pack extra clothes if you wear your dress to the park because you’ll probably want to take it off later. Don’t wear it all day, especially if it starts to get uncomfortable. Cut off all the tags and labels because those rub against your skin and it hurts.