Protect your shoes by wrapping them in T-shirts if you don't have shoe bags. Roll sweatshirts and undergarments to fill space. A full bag helps keep the contents from sliding and wrinkling. Coordinate your wardrobe around one or two basic colors. This will automatically eliminate many items of clothing.
Separates are best because they can be mixed and matched.
An old travelers trick is to lay out everything you'll need, then take half and return the balance to your closet. Minimize wrinkling by packing shirts buttoned. Fold clothes as little as possible. Be sure to fold them close to the waist and the seam. Place plastic dry cleaner's bags around clothes to minimize wrinkling.