A clove hitch is considered one of the four primary maritime knots and being able to tie one should be included in your survival skills. The clove hitch is essentially two successive half-hitches around an object. It is simple to tie and can be used to secure the end of a rope to an object and is most effective when tied to a round (tree, post, etc.) or cylindrical-shaped object (pipe, barrel, etc.).
It can also be easily tied in the middle of a rope in order to secure a line to a carabiner.
The clove hitch has another distinct advantage. With a little practice, it can be tied quite easily using only one hand. This is important should you suffer an injury that leaves you in the position of only having the use of one hand. When you can tie a clove hitch to the index finger of the hand you are using (right or left), you have mastered the ability to tie a clove hitch one-handed.
A great resource for learning how to tie a variety of knots properly can be found at http://www.netknots.com/. They offer different sets of knot cards at a very reasonable price. The knot cards can be easily carried and used for reference purposes to insure your knots are being tied properly.
Got survival knots?
Staying above the water line!