Introduction to Cryptics by Barry Tunick
About the author:
For several years Barry Tunick was the regular cryptic constructor for Verbatim
magazine and the regular Double-Crostics constructor for Saturday Review .
His puzzles have appeared in many magazines, anthologies  and newspapers.
Tunick's crossword-writing partner of 19 years is Sylvia Bursztyn, with whom he has
constructed the last 1000 Sunday Los Angeles Times puzzlers.  These crosswords have
been the basis of more than 20 Random House anthologies.

Introduction
Certain cumulative small feelings of accomplishment make the cryptic form more
stimulating than conventional crosswords (which I'll refer to as "crosswords").   Cryptics are
like jig-saw puzzles, providing continuous consecutive successes, rather unlike life.  These
"aha!" reactions make them a satisfying intellectual recreation.  
Crosswords share this feature, but cryptic "aha!s" are more satisfying than
crosswords' because the struggle to achieve them has been more sophisticated.  Most
crossword clues ask for synonyms from your memory, but cryptic demand  some form of
mental gymnastics.  You could say that each cryptic clue is a puzzle in itself.
A little-remarked advantage of the genre is that not having to cross every letter gives
the constructor the chance to use a greater variety of words.  Such usual crossword suspects
as One, Ore, Assess and Essene (and the never-popular Proa and Anoa) are largely absent
from cryptics.

Some Cryptic Crossword Conventions
Almost every clue has a straight definition or synonym as one part and a pun,
anagram, container, etc. as the other.  Occasionally you'll find two straight parts; less often,
two cryptic ones.  The straight definition may come before or after the cryptic one; it's not
always easy to tell.  Sometimes a brief pun or quip is the only clue.
The main rule is to consider words as assemblages of letters and sounds even more
than as units of meaning.  The general rule is "Mental re-punctuation of all clues is a
necessity."  Don't take punctuation, capitals or spacing too seriously.
The best cryptic clues have a smooth and sensible "surface" meaning; one
suggesting a reasonable scenario--albeit one that usually has no connection with the
solution.  For example, the clue "Spoils comeback drive" has a clear sense, one connected
to sports.  But as the bard said, "But you know, sometimes words have two meanings."
"Comeback" indicates that a word is to be reversed.  A synonym for "drive" is "tool," which
reversed gives the answer:  Loot (a synonym for "spoils").

Main clue categories (Keep in mind that a clue may incorporate more than one):

Anagrams:
You know how to anagram, don't you?  Just put your lips together and HIT
"SLEW"--or LEW''S HIT or HE WILTS or WHITE L'S or THE W  IS L.  The
anagram may be the whole answer word, or just part of it. Suspect that an anagram is
involved if the clue uses a word implying movement, irregularity,  uncertainty or disorder:
Troubled, chaotic, dancing, perhaps.  E.g.
Possibly solve it in bed? = Violets (in bed suggests flowers)
Ben's camel is odd in appearance = Semblance
They might be one's trial = Relations

Double Definitions:
A double-def clue gives two definitions for the answer word.  The
clue may be only two words:  
Unnatural dwelling?  = Flat
60 per minute? Not so good = Second rate
Springtime 2000? = Leap year

Concealments:
An answer may be found using part of one word in the clue and part of
the next:
Canaletto picture reveals the subject = To pic
Found all a senator's letters in Texas city = D all a s
French composer's in "L'Alouette" = Lalo

Reversals:
If a clue contains a word like "up" or "north" (for a down clue) or "back" or
"westward" for an across, suspect a reversal.
Mercenary go up lane five = V  enal (lane is reversed)
A cap thrown up; he's joining the tribe = A pac he (cap is reversed)
Old beast chases Uncle back to Russian river = Mas to Don (uncle = Sam)

Charades:
Part of a clue is for the first part of the word; the second for the second
part, etc.
Composer gives many an offer of a lift = C hop in
Don't blame the old single speed = Ex one rate

Containers:
The answer to one part of a clue may be nested in another one:
I love to be in a play--or pictures = D I O rama (I love is in drama)
Make departure in art, in a manner of speaking = Ar go t

Homophones:
Phrases like "to the ear,'" "orally" or "one hears" tip off that the solution is a
homophone:
Quoted as seen and located by sound = Cited (from sighted and sited)

Puns:
These plays on words are usually single definitions:
He's taking stock = Shoplifter
But they can be more complex:
It put Smith, that mighty man, in the shade = Chestnut tree
The user of this revolver could get a jar = Potter's wheel

Miscellaneous:
Sometimes single letters are indicated by terms like Capital of Kansas (for K),
Beethoven's Fourth (T), Poles (N, S), points (of the compass: N, E, S, W).
Heart of Spain is A.
Right and left might stand for R and L; hot and cold for H and C.  A number might
be its Roman equivalent (10 = X; 50 = L; many could be C, D or M).  Love, ring, nothing
or circle could be O; as could hug (as in XOXOX, where X = kiss).  K could be shown by
strikeout, 1000, karat or kindergarten.
Two or more letters could be represented as by abbreviations for states or months,
or in this way: Half dollar = dol (or lar); Most of Peru = Per or eru.