I don't see enough people talking about this, but these points have been crucial in my own journey of self-typing and typing others, so here we go. Before you type yourself, consider:
The degree of stress you're under right now: Stress greatly influences how you view yourself, or if you have enough objective self knowledge to have an honest assessment of your own type. While a normal amount of stress brings people into their strengths, continued stress actually pushes you into the worse parts of your personality, and this experience can last anywhere from a few hours to (in borderline-traumatic cases) decades. And it's not an objective assessment of your type if it is only decided based on how you are at your worst. your type is a mixture of your general thought process, your worse tendencies, AND your better choices.
Possible general or trauma-induced dissociation: A lot of people have a general tendency to dissociate for internal or environmental reasons. it's WAY more common than we think, and it happens in varying degrees of "this trait upsets me so i pretend i don't have it/this trait makes me happy so i own it as a defining part of my personality" to "i do things that enrage and/or surprise me, i don't know where these thoughts and behaviors come from, and i'm helpless in controlling them so in my good days i pretend that they don't exist and get shocked/upset when people point them out to me" cases, counting out DID since that one is the obvious case. People tend to have more dissociation towards the parts of their psyche that resides in the [MBTI] tertiary and inferior functions, or the [instinctual variants] blindspot, oooor [in an enneagram sense] the parts of us that keep us from achieving the ideal image we aspire to have, but this isn't always the case. And to have an honest view of yourself, you have to keep in mind that at all times you're a little, or a lot, dissociating from parts of you that is unpleasant/scary/sad to think about, and that it's not only okay, but necessary to be open to feedback, new experiences and new insights regarding yourself. Fear is an inseparable part of self discovery, so before trying to type yourself, you have to learn to be comfortable with fear and be able to sit with it and learn from it. You don't have to 'accept' whatever comes your way and whatever new thing you discover, but you have to be able to entertain possibilities and get comfortable with the uncertainty and complexity that comes with being a human.
Mental illness: this one kinda goes without saying, but mental illnesses of all kinds (or generally being stuck in fear responses) narrows your focus on a very limited number of mental tools you have learnt since childhood for dealing with a shit life. They make it very hard to be present to your whole personality, not what you constantly resort to in times of (perceived or real) crisis. It's not impossible to type yourself when you have mental illnesses, but it makes the process longer, and you need to have more patience and compassion towards yourself.
Your gender: It actually really fucking matters, how you're raised based on your actual or perceived gender, or even the gender your caretakers proffered you to be like. Your own personality and preferences are only a small part of the choices you make throughout your life, and another part of that process is how others react to you and the choices you might make. In some cases, even though your preferences are right there, you may make different choices because there's more reward and acceptance for that choice, even though it's not your actual preference. Or you may make choices because the consequences you'll face for not making them are so high and dont seem like they're worth it. A lot of women don't entertain the possibility of being a thinker because as women they're conditioned to think that they suck at rational decisionmaking and have a natural knack for emotions and dealing with them. As a byproduct of that conditioning, many thinker women have higher emotional awareness and are more in touch with their emotional side than men of the same type - simply because there is a lot of social shaming and pressure on women to be sympathetic and considerate and to be able to emote. A lot of feeler men actually have less healthy thought frameworks and tools around emotions then women of the same type, as society does not expect men or train them for emotional intelligence and thought frameworks generally associated with femininity and women stuff. SO blind women are often more accommodating and mindful of how they're perceived than SO blind men, SP blind men often have more attention to SP and develop more tools in dealing with SP-related works, etc etc, the list goes on forever. The thing to keep in mind is, toss out the stereotypes. Don't dismiss different possibilities simply because "you're not as emotional as the feeling type descriptions suggest" or "you're not as edgy as the SO blinds you've seen" or “you have some hobbies you love dearly so you must be a SX variant”. Different descriptions are written with the majority of that type in mind. They're ripe with stereotypes, and for a good reason. But you don't have to fit with stereotypes to be a type, you just have to share the thought process and the inherent preferences that create its mindset.
With all that said, what is the best approach to self-typing?
Observe yourself when you're in flow state. When you're content, happy, feel safe, and are surrounded with people who accept you and love you for who you are, no matter what it looks like. If you cannot find a context in which you feel like that, imagine yourself 5 years from now, in a context that gives you those feelings. What would you look like if you were surrounded by accepting, loving, sincere people who accept you no matter what and find you enough in and of yourself? imagine that scenario in full details and make note of the choices you would make in that context.
Make notes of what you have generally thought most of your life, before you had mental illness. Be open to any and all thoughts that might come up.
Learn to love yourself before you try to self-type. It's hard to type yourself correctly if you're consciously or subconsciously fighting against parts of you that you consider weak/unacceptable/not enough/boring/problematic/wrong. Be open to your own thoughts and other's feedback and before you try to decide what type you are, decide that whatever comes up is okay, is cool, is enough, and there's nothing wrong with it. Shame and judgement is the enemy of objectivity. consciously decide to accept and offer compassion to yourself. If you cannot seem to do that, imagine an anxious dear friend of yours, and write down how you would treat them and what you would tell them. Now do those stuff for yourself to the best of your abilities, and tell those things to yourself.
Move beyond typing. Ask yourself why do you want to type yourself, what does it offer you, what purpose do you have in trying out these labels. Do not self type when you feel insecure, sad, depressed, isolated, rejected. Labels are not what you need in those moments, it's kindness and acceptance of who you are.