Maroon and Gold are the colors of Gryffindor house, and you'll need to show them off on the tie, scarf and robe.
Start out with a gold tie. Use red fabric paint to add the lines on the tie. If you're using paint and a brush, employ a ruler to help you make straight lines. A fabric pen works much easier in this case and most fabric stores have them in many colors. Make two thick lines, then skip an inch and make a very thin line. Skip another inch and repeat this pattern.
Hermione's hair is on the wild side as a child, her puffed wavy and sometimes crinkly locks can be recreated right out of the shower. Hang your head upside down while it's still wet. Blow dry your hair while scrunching it with your hand. Rub a dime sized amount of styling mousse on your hands before grabbing clumps and pushing them against your head. Use a towel to pat clumps of hair against your head to help curl and dry the hair. Once dry, stand up straight and behold your raging afro. Tame it to a nice Hermione volume with some more styling mousse.
Any thin stick can be made into a wand. Peel off any bark and use a piece of sandpaper to smooth down the sides of the stick. For a pointed end, use a small knife to whittle the end of the stick. Shaving the end of the stick should be done with adult supervision. Apply a dark or light wood varnish to your smoothed wand.
You could also use about.com DIY Fashion's Easy Pencil Wand for kids, or one of the many wand tutorials available on Leaky Crafts in the Woodwork and Other Crafts sections, or spring for a toy Harry Potter wand.
The Leaky Cauldron's Harry Potter Crafts jewelry section has two excellent tutorials available to choose from to make yourself a time turner for your costume.
Look in your local thrift stores for a white button-down shirt and a black or gray vest to wear over it. Wear a pleated black skirt, knee-high socks and black dress shoes.
Mary Janes work nicely for your feet.
This tutorial was taken with permission from about.com's DIY Fashion section.