When character typing, choose a system and stick to it, since various systems interpret the functions in different ways. Read as much as you can get your hands on from a decent published (credible) source, since there is a lot of misinformation online.
If you can get a copy of Lenore Thomson’s Personality Type, she is a good resource and the one whose information comprises the majority of this Basic Typing Guide.

Rule 1: Assume the character is a sensor.
New typists are too quick to label characters as intuitive. An intuitive character will stand out because they are motivated by hunches – they know things, or connect things the other characters do not or find of little interest. Unless this defines their personality in an identifiable way, assume them a sensor.
Rule 2: Form a decent argument with “proof” based on an understanding of the functions.
If you find yourself grasping at straws or being overly vague to explain their functional stack, either a) you have the wrong type, b) you do not know the axis very well, or c) the character is poorly written.
Rule 3: Do what works for you.
Some people type based on the big picture (this character acts most like an ____, so they are one); some type based on details (careful assessment of the character, gathering facts); some type based on a combination of both, or use a conclusion and work backward to find the evidence. If you cannot figure out a character, it may be you are holding too tightly to an assumption; throw out that type and consider another one.
Rule 4: Be patient.
Typing takes practice. Learning and deepening your understanding as you type will show you the mistakes you make and give you additional information and clarity about the functions. Avoid forming ‘dislikes’ for certain types and assume no character shares your type unless you can see clear evidence of how they ‘fail’ in the same cognitive ways you do. Let go of biases, expectations, and learn to identify, appreciate and admire each type for its strengths.

My Typing Guide
(If you are stuck, need a refresher, or to consider another type, you can reference my condensed overview of each chapter in Thomson’s book that reminds you of a function’s focus and behavioral attitudes.)
Cognitive Shortcuts List:
NJ: High Introverted Intuition (Ni) / Low Extroverted Sensing (Se): Big picture thinking, reflects on meaning and implications, singular conclusions, personal vision, firm on their perceptions, long term plans, strategy, flexible but decisive. Bad at improvising, often miscalculates, over-indulges, unaware of environment.
SP: High Extroverted Sensing (Se) / Low Introverted Intuition (Ni): Quick to react or instigate action or to respond to novelty or change, opportunism, in the moment, quick action, sensory confidence, risk-taking, hands-on, makes things happen, impulsive and not often careful. Fears impending doom, fails to plan ahead, misreads situations, fixation on a single goal.
NP: High Extroverted Intuition (Ne) / Low Introverted Sensing (Si): Big picture thinking, good at improvising or changing their mind, loves wit or puns, inappropriate humor, optimistic dreamer, new patterns, following new thoughts. Physical detachment, underestimates projects, nitpicks about change, fails to be realistic.
SJ: High Introverted Sensing (Si) / Low Extroverted Intuition (Ne): Grounded, detailed, good with routine, sticks with what they know and cherish, observant, aware of physical needs, careful decision making, prefers sensory comfort, details, precision, personal experience, trust in past precedent.Fearful of consequences, unable to sort possibilities carefully, doesn’t see or give much thought to what’s going on beneath the surface, gives in to irrationality, becomes impulsive under stress.

FJ: High Extroverted Feeling (Fe) / Low Introverted Thinking (Ti): Emotionally persuasive, maintains good relationships, smooths out discord, uses collective values to connect with others, good people skills, prone to sharing feelings, focus on social appropriateness, projects ‘false’ moods, need to be liked. Disconnects from others, indulges critical or mean judgments, forms rigid logical conclusions, becomes frustrated by problems and fixated on “why is this happening?”
TP: High Introverted Thinking (Ti) / Low Extroverted Feeling (Ti): Detached and analytical, systematizes information to understand how to problem-solve or prevent/avoid problems, swift action, learning as they go, investigative, critical, curious how it works, consistent internal logic, desires understanding. Sometimes loses their temper, impatient with people and their feelings, unsure of their own emotions, disregards emotional ‘data,’ low-order emotional manipulation, annoyed by feelings.
TJ: High Extroverted Thinking (Te) / Low Introverted Feeling (Fi): Sees a problem and wants to resolve it efficiently, offers useful factual information but frustrated by incompetence, immediate observable logic, financially driven, organized and efficient, detached from problems, reliance on facts. Situational empathy, strong emphasis on personal responsibility, repressed feelings, discounts their own or others’ feelings.
FP: High Introverted Feeling (Fi) / Low Introverted Thinking (Te): Reflects on their feelings, acts in accordance to their moral instincts, seeks to alleviate suffering, sensitive, empathetic, honorable, strong moral judgments, need to be true to self, internalized emotions, must do what is ‘right,’ emphasis on fairness. Can be a dictator under stress, struggles to rationalize or form factual arguments, blunt and authoritative, acts on feelings, refuses to make detached decisions.

Enneagram Typing
Focus on what they appear to want most (their motive) and how they typically behave toward themselves and other people. You can learn much more about the Enneagram types on our corresponding page.
Anger / Gut Center (how I handle my anger):
1: repressed, buttoned up, right / wrong, morals, rigid.
9: easygoing, peaceful, complacent, passive, calm.
8: aggressive, assertive, controlling, confrontational.
Image / Heart Center (how others see me):
2: helpful, a rescuer, of service to others, moves ‘toward’ them.
3: focus on success, ambition, competitive, workaholic.
4: moody, self-pity, self-indulgence, morose, romantic, moves ‘away’ from others.
Logic / Head Center (how I avoid my fears):
5: intense, cerebral, book knowledge, detachment, dismisses feelings, objectivity.
6: anxious, loyal, worries, self-reliant, suspicious, humorous (cp6: attacks, assertive, may look like an 8 but will back down under pressure / is fearful).
7: optimistic, playful, busy, seeks pleasure, impulsive, witty.
The character likely displays two strong Enneagram types; when you have narrowed it down to two, ask yourself how they react under stress and what seems to govern them most to determine their core. (For example, Rodney McKay from Stargate Atlantis is a 3-6 combo; he is paranoid, insecure, angry, and defensive under pressure like a 6, but most of the time is arrogant, ambitious, assumes he is a genius, and wants praise, ergo a 3.)
Overall, have fun with it, don’t take it too seriously, and enjoy the process!