Most of the time, we will be emptying our kayak on the river side after a swim.  Hopefully you remembered to install flotation in the rear of your boat.  Always remember that water is quite heavy at 8 pounds/gal.  The first step is to remove the drain plug if your boat has one.  To avoid losing a drain plug, I tie a thin piece of nylon, sewing thread, or fishing line through the plug and around the grab loop.  If you haven't done this, put the drain plug in your pocket.  The next step is flipping the kayak from the side so the cockpit faces downward.  This will remove most of the water.  Now you want to push one end of the kayak well up on the river bank so it sits higher than the other end.  You can now lift the low end using your leg muscles and rock up and down to nearly all water is drained.  For the final touch, place the empty drain end on land and hold vertical so the remaining water drains through the drain plug.  Don't forget to attach the drain plug when finished.  For the Felix Unger's amongst us, tilt the boat on its side and sponge out the remaining moisture.

If you have a heavy boat and need assistance, don't be shy - ask for help.  Also, if you had a long cold swim it is always a good idea to ask for assistance.  When you are chilly, your muscles don't work as well and you don't want to injure yourself.

The following article does a nice job at describing the procedure: Emptying Your Kayak.  Here is a very humorous alternative method: Cool Way to Empty a Kayak.