The most efficient way to pack a suitcase is to lay everything out on the bed prior to packing and make a plan.  All clothing should be stacked in layers in the center of the suitcase creating a neat square clothing pack.  Allow room on all sides to fit everything else.

Shoes

Place shoes in a bag.  Each shoe bag packet can be wedged in between the suitcase edge and the clothing square.  If you are packing high heels be sure to face those toward the clothing stacks so that there is no chance that they will puncture the bag during travel.

Shirts/T-Shirts

Lay the shirt flat and hand brush to smooth.

Fold the right side of the shirt from the sleeve seam toward the center of the back of the shirt.  Do the same with the left side. If it is a long sleeve shirt lay the sleeves flat and smooth.

Fold the shirt in half bringing the top collar to the bottom shirttails.  Hold the vertical folds in place.  Fold in half again.  Brush to remove wrinkles.

Socks/Hosiery

Roll socks and underwear and tuck them around the edges of your clothing square.  Hosiery should be placed in a bag such as an empty makeup bag to avoid runs and snags.

Packing a Hat

Hats can easily become crushed when packed in a suitcase during travel.  To maintain the shape of hat fill it with clothing such as socks and place it brim down in the center of the suitcase.  Pack all other garments securely around it. 

Toiletries

Place all toiletries in a heavy-duty toiletry bag.  It's worth the investment to purchase a bag that will not puncture, tear, or come undone during travel as a mishap could not only ruin your trip but permanently damage your clothing as well.  The toiletry bag can be wedged in between the suitcase side and the clothing square.

Laundry Bag

Packing a laundry bag to use as a hamper for the dirty clothes will help to keep you organized.  With this method you won't be digging through a pile of socks attempting to figure out which are clean and which are dirty.  It is also a great timesaver when you are ready to unpack at home.