1) Learn the Eitz Chaim (Tree of Life) of Isaac Luria Ashkenazi. [No introductions. Just the actual book itself. Introductions are a waste of time at best and mostly pervert the meaning of Isaac Luria.]
If possible, learn it with Talmud and Musar. But even by itself the Tree of Life of Isaac Luria is an amazing masterpiece. And it is different from other masterpieces in that it has the ability to open up the higher spiritual worlds,- if one learns it in the right way.
The other writings of the Ari [abbreviation for HaElohi Rabbi Isaac Luria]--the Pri Eitz Chaim and the Shemona Shearim [Eight Gates] are good, but without the background of the Eitz Chaim are not possible to understand.
2) A word of warning: All books of chasidut on Kabalah written after the events of the time of Shabatai Tzvi (note 6) borrow a lot from Shabatai Tzvi and his false prophet, Natan. Even when they are not crypto followers of the Shatz [short for Shabatai Tzvi], they unknowingly use his basic approach to Kabalah.
So it is important to give people an idea of which books were not affected by the teachings of the Shatz, and thus can be learned and studied without fear of being infected by the terrible virus (in a spiritual sense) that affected the Shatz.
The books of Kabalah that were unaffected by the Shatz and have no secret teachings which stem from the Shatz are Sefardic. That means Rabbi Yaakov Abuchazeira's (note 1) books and Shalom Sharabi's (note 2) are all highly recommended. Almost all books of Kabalaist type of teachings in the Ashekenazic world after the Shatz are full of interpretations that come directly from the Shatz, even though I think this happened unintentionally. [But in these sensitive areas intention does not mean much. A mistake is still a mistake. It is just like a mistake in making a bridge in which it does not matter how well meaning the student is. A mistake is still a mistake.]
[I just know that people are wondering about the Ramchal (note 5) and Komarna. I think they are OK, but it is safer to go with the Sefaradi books I mentioned above. I hate to say it, as I myself am Ashkenazi, but in this case the Sefardim got it right.
Notes
(note 1) Rabbi Yaakov Abuchatzira wrote many books and a lot do not deal with Kabalah at all. But there are books in which he deals with some Kabalah and they are excellent.
(note 2) The Nahar Shalom by the Reshash [short for Shalom Sharabi] has a vast system based on modifications that the Ari added towards the end of the Eitz Chaim and the famous Drush HaDaat.
(note 3) Pri Eitz Chaim is a book by Reb Chaim Vital about how to apply the concepts of the Eitz Chaim to prayer
(note 4) The Eitz Chaim is the text from Isaac Luria which gives the basic structure of all the higher spiritual worlds.
(note 5) Rabbi Moshe Chaim Lutzato, author of the famous Musar book, Mesilat Yesharim (note 6) The Shatz was a false messiah. His follower Rabbi Nathan in Israel was a tremendously and famous, brilliant, scholar of Talmud and Kabalah wrote very influential books on Kabalah that initiated approaches and ideas in Kabalah that were and still are widely accepted by Ashkenaic Jews.
Perhaps a bit more detail is proper here. The Shatz was basically weak minded Baal Teshuva. When he came to the most famous tzadik Hador in those days Nathan from Gaza, Nathan told him that he is the messiah. I mean how would you react if you got an interview with Reb Moshe Feinstein and he told you that you are the messiah? After that this Tadik and the Shatz were accepted by 99% of world Jewry as being the promised Messiah. Just by mentioning the name of the Shatz people did amazing miracles all over the world.--Witnessed and recorded and notarized. Even up to the revival of the dead. This was even in places that people never saw the Shatz. After he became an apostate the Jewish people went through a period of great regret and there was a purge of all documents that could tie anyone to that movement.
Appendix
) The Tzadik of Komarna wrote a kind of running commentary on the Five Books of Moses based on the Ari'zal and to me it looks very straightforward and kosher.
) The student of The Vilna Geon, Reb Chaim from Voloshin has a book called the Nefesh Hachaim which is the best of all Kabalah based books to come out of the Ashkenazi Jewish world .
) There are dangers of learning Kabalah for people that are not properly spiritually prepared, even authentic Kabalah. All the more so is there danger in learning Kabalah that is not authentic.
) kabalah is best learned as a part of a normal Torah curriculum, Babylonian Talmud, The Yerushalmi Talmud, The Poskim Rishonim i.e. the Rif the Rosh the Tur and the whole Shulchan Aruch with all its commentaries with the writings of the Ari .
I think that Musar is important. But Musar is a highly limited tool in character correction. (Musar means books of classical ethics based on the Torah and Talmud.)
And then I think about Kabalah. And it occurs to me my own very inspiring experience with learning the writings of Isaac Luria. And then it occurs to me the effect I have seen Kabalah usually has on people.
And then I think about the Gemara, Rashi, and Topsphot. Also I think about my experience and then I think about other people's.
My suggestion is to learn the written Law along with the oral explanation-- the Mishna and the Gemara.
Also Musar [Ethics] for character improvement.
Also Kabalah after doing the Talmud a few times. The reason is that without Kabalah it is very hard to see what is going on inside of the Torah. I mean to say the we Jews think that the Torah is divinely inspired, and that it hints to great hidden wisdom. But it is hard to see any of that wisdom on the surface level. So Kabalah is an attempt to scratch the surface of the Torah to discover its hidden depths.
Kabalah has a bad name by gentiles as if it is some kind of magic. If that would be what it is about, then their critique would be justified. But that is not what it is about at all. When you sit down to learn Torah whether the Oral or written Torah don't you wonder what is the deeper meaning of the stories about Abraham, Isaac, Yaakov? That is what people like the Gra {The Villna Geon} Isaac Luria, and Moshe Kardovaro, and Shalom Sharabi wanted to understand.
However Kabalah is at best a commentary on the Oral and Written Law. It is not meant to take the place of Talmud learning and it was never intended to do so. And at this point it is important to justify the Oral Law.
What is is and why is it necessary?
When we come to look at the Written Law/the Old Testament we find the first issue that confronts us is that of interpretation.. How do you resolve things that look like contradictions? Or how do you solve the problem that sometimes a verse says things that could have been said with less words. What are the extra words for? When we assume that this document is divinely inspired we have to know that there is a good reason for every word. This is the place of the Oral Torah. That is to resolve these issues. The Talmud does not claim to be Divine. It only claims to be a rigorous examination of the verse of the Torah and the highly human attempt to get one coherent doctrine out of it. It assumes that it is not open to individual interpretation. It is meant to be a book of Laws for the Jewish people. and no law book is open to individual interpretation.
How would it look in a court of Law if the defendant could say to the judge Your honor I am afraid you interpretation of this law about murder is incorrect. In fact it does not mean what you say at all. It only means not to murder unless you are angry and can't help yourself.
___________________________________________________________________
Also I think it is important to make a difference between the idea of a tzadik and the idea of the written and Oral Law.
The tzadik/saint is not supposed to be a replacement for the Torah. However we also know that it is common in Breslov to conceive the Tzadik/saint as being the central issue.