Decide on a color scheme and basic theme of your tea party hat before purchasing your supplies. If you are doing this for a group activity, purchase a variety of colors and decorations.
Place your plain hat on a flat surface. Before gluing anything onto the hat, place your decorations where you think you'll want them. This is the time to move things around.
Cut a 1-yard piece of tulle if you want to have a veil on your hat. Glue one side of the tulle to the brim of the hat close to the crown. You'll cover this with other decorations later, so don't worry about the glue showing. This is all you need to do if you only want a veil in front. If you want one in back, glue another 1-yard piece of tulle to the back.
Measure the circumference of the crown base and add enough length of ribbon to wrap around the crown and tie a bow. Glue the ribbon to the hat to keep it from slipping.
Position the flowers you've selected on the brim of your hat. You may have them nestled close to the crown and leave some of the brim exposed, or you may cover the entire brim. Before gluing the flowers to the hat, lift it and make sure the weight of the flowers doesn't cause the brim to sag more than you want. Once you have the flowers in place, glue them to the hat.
Add other decorations, such as tiny fake birds, birdhouses or fruit. Glue them down securely.
Tuck and glue some feathers, ribbon or bows around your hat to give your creation a finished look.
If you want a decorative way to keep your hat in place, cut a 2-yard piece of tulle, bunch it up and glue the center of it to the top of the crown. Bring the tulle loosely down over the decorations and tie it beneath your chin.
The more elaborately you decorate your hat the better.
Add gloves and a parasol, and you'll be the talk of the tea party.