In order to truly understand any particular Hasidic group a number of factors are involved. You need to know their teachings, their tales, their style of prayer, and their niggunim (music).
Though Hasidism has developed many different sects during the course of its almost 300-year history, there are certain teachings that remain central to all. Worshipping God joyously is one of these. The centrality of music and dance to Hasidism is an expression of this. The powerful and enigmatic Rebbe Menachem Mendel of Kotzk took a famous rabbinic statement and used it to illustrate this point. In the Talmud it says that “when the [Hebrew] month of Av [during which both ancient Temples where destroyed] arrives we diminish our joy; when the month of Adar [in which we celebrate the festive holiday of Purim and a month after which we celebrate Passover] arrives we multiply our joy.” The Kotzker Rebbe adds, “but always joy” (Tractate Ta'anit 29a).
The phrase in Proverbs (3:6) “In all your ways know Him [God]” is fundamental to Hasidism. Included in this verse are two major themes. One is the goal to live in a state of union (devekut) with the Divine as much as possible. The other is to sanctify your entire life through your activities. This is called avodah b'gashmiyut (worshipping God through the physical). In this manner we can raise the sparks (nitzotzot) of Divinity and holiness that are in everything.
Menachem Mendel of Kotzk reinterpreted the verse of Psalm 81:10 that “you should have no strange god among you” to also mean that “God should not be a stranger to you.”
The perspective that there are sparks of divinity in everything affects the way we relate to the world. It gears the intention of our actions and thoughts toward raising up those sparks. It renders all of our actions of vital, even cosmic, importance, for we can bring holiness into the world and hasten the messianic era through our attention to the Divine that fills everything. Just as any person we encounter might be the Messiah, the Divine spark is in everything even if it is not obvious to us.
Hasidism emphasizes, as does Judaism in general, the spiritual life that is lived in community, as Hillel is quoted in Mishnah Pirkei Avot: “Do not separate from the community” (2:5). Hasidism, with few exceptions, tends to avoid asceticism.
Ya'akov Yosef of Polnoye had ascetic tendencies when he met the Besht. The Besht told him a parable about once driving a carriage with three horses, none of which was neighing. A peasant told him to loosen the reins, which he did, and the horses began to neigh. Ya'akov Yosef understood that the soul too needs to have the “reins” loosened.
While Hasidism discourages self-denial, it also frowns upon overindulgence in the physical. It attempts to sanctify our physical activities by focusing on the spiritual through them. There is also the ideal of totally transcending the physical, which is called hitpashtut hagashmiyut. This may occur most easily through prayer, music, dance, or the study of Torah for its own sake (Torah Lishmah, which means to study Torah not to achieve anything such as recognition or reward, but to study purely for the love of God and Torah).