Although misdirection is fundamental part of cryptic crosswords, I've put the section near the end because it can be tough to get one's head around. However, if you have been working through the guide in a linear way, you should have encountered misdirection without my having explicitly discussed it and have an idea of how it works already.
The idea of misdirection is to take the solver's eye off the ball rather like a penalty taker in soccer looking at the left side of the goal when she will shoot at the right. There are many different types of misdirection and the following sub-sections should give you an insight into the types you will find in almost every cryptic crossword.
Surface Reading Misdirection
At the beginning of the guide we touched on misdirection briefly with the clue:
Capital city in Georgia (6)
... here the clue seeks, through its surface reading, to misdirect the solver into believing it is a straight definition and that the CAPITAL CITY IN GEORGIA is the answer being sought, rather than a CAPITAL CITY and a CITY IN GEORGIA, USA.
This is a simple surface deception and you will find many clues like it in cryptics. A clue's surface will almost always try to misdirect you, if not by leading to a totally different answer, then by making it difficult to find the definition.
The setter can use indicators (words that show the solver they need to perform an action on a word) to deceive, too. Often they do this by constructing a clue that has several possible indicators in it. By doing so, it makes it difficult for the solver to know how to start to unravel the wordplay.
Here is an example:
Auction of old tesla coils (not in working order) (3,2,6)
auction of - 1st piece of anagram fodder
old - O (abbreviation for old & 2nd piece of anagram fodder)
tesla - T (a scientific abbreviation for the tesla unit & 3rd piece of fodder)
coils - anagram indicator
not in working order - definition (OUT OF ACTION)
(OUT OF ACTION*)
... here we have three potential anagram indicators in COILS, NOT, and WORKING as well as one potential wordplay link in OF. By including many possible indicators the setter attempts to misdirect the solver into anagramming the wrong piece of fodder, or into believing that AUCTION on its own is the definition because OF is such a common wordplay link.
Part of Speech Misdirection
A part of speech misdirection works by having a word in the surface of the clue in one part of speech, but a different part of speech in the cryptic reading.
This can be tough to get a handle on at first, but hopefully I have primed you with the very first example of the guide. Let's remind ourselves of the clue to see how a part of speech misdirection works.
Career knock for cop found napping on the job? (5,4)
career - speed
knock - bump
for - definition link
cop found napping on the job - definition (speed bump)
In this clue, the part of speech misdirection is with the first word CAREER. The surface of the clue makes it clear that CAREER is a noun meaning JOB. However, in the cryptic reading of the clue CAREER is a verb meaning 'to speed'. The misdirection aims to force the solver to see CAREER only as a noun and seek synonyms like JOB, OCCUPATION etc.
This device is used by the setter to throw the solver off the scent by capitalizing a word to make it look like a proper noun. By doing this, the setter can disguise a word's part of speech in the cryptic reading or just misdirect the solver as in the following example.
Managed to crash Club Lolly in Geneva (5)
managed - ran
to crash - insertion indicator (as in 'to gatecrash')
club - FC (abbreviation of football club)
lolly in Geneva - definition (FRANC - lolly is slang for money)
In the above clue, CLUB and LOLLY are falsely capitalized. By doing this the split between definition and wordplay is harder to spot. The setter hopes the solver will, for a little while, think that either MANAGED or GENEVA is the definition. This technique leads us nicely into the next section.
NOTE: In most cryptic crosswords the setter may falsely capitalize a word, but to falsely decapitalize a word that must carry a capital letter is not allowed.
Lift and Separate
The lift and separate is a deception that aims to make it very difficult for a solver to separate wordplay parts by putting them in a well-known collocation:
Force field - none shall pass its energy (4,2)
force - definition (lean on)
field - lea
none - subtraction fodder
shall pass its energy - E subtraction indicator (Energy has an E abbreviation in physics)
Note how the term FORCE FIELD is a two word noun in the surface. Because of this, the setter hopes the solver will read it as such and not see (for a while at least) that the two words needed to be lifted and separated from their current reading to split them into definition FORCE, and first part of wordplay FIELD.
Also note how, by employing an em-dash after the two word term, the setter seeks to further strengthen the deception that the two words are to be read together
Single Word Misdirections
Rather like the part of speech deception, indicators can also be used to deceive the solver because they can mean more than one thing. Take ABOUT, for example - let's look at what it can mean in a cryptic crossword:
About as abbreviation:
A - about
C - circa
CA - circa
RE - regarding
About as indicator:
About as a synonym:
TO DO WITH
All these different meanings enable the setter to construct a clue which uses ABOUT in such a way that the solver is sure it is acting as an anagram indicator when in fact it is simply indicating the letters CA.
Tricky types these setters, eh?