The basic tenet of Sufism comes from a hadith (saying of the Prophet, peace and blessings be upon him): "I was a hidden treasure who longed to be known." The focus of Sufi initiates is to know God-to get closer to God with every breath.
Sufism is made up of many different schools, or orders. Each focuses on different types of practices-there are orders that focus on visions and dreams, ones that focus on healing, ones that focus on the universality of faith-that all paths lead to God.
Sufism is initiatic. You must request permission and then be initiated by a Pir, Shaykh, Murshid, or guide. When you are initiated, it is more than a blessing; you are connected to all the teachers of that lineage, and they can guide and help you along your path.
One can belong to more than one Sufi order, and many initiates are members of several. The main connection you have, however, is to your guide. That guide is your personal spiritual consellor. He/she is not a 'guru', but rather someone who is a few steps further down the path. Guides give the initiate practices to do-these can involve sacred phrases, breath practices, and walking practices.
One practice that is done by all Sufi Orders I know is a ceremony called 'zkr'. The word means both 'remembrance' and 'repetition'. It is reciting sacred phrases, the most common used being "La illaha il Allah", or "there is no reality save the One". This can be chanted, sung, whispered, even shouted, depending on the way a particular order does the ceremony. It can be done seated or standing, moving or still. The 'whirling dervish' ceremony is a type of zkr done by the Mevlevi Order (a special type;Mevlevis do other types as well). All zkrs I've been to have been open-one does not have to be an initiate to participate.
My main order is the Sufi Order International, specifically Murshida Tasnim. Besides doing the practices described above, Murshida does the Dances of Unversal Peace, moving meditations that honor all the world's spiritual traditions.
Our prayers, done three times a day, are in English, believe it or not, and they honor all faiths.
To find out more, check out these websites:
Murshida Tasnim's is at
http://www.churchofall.usSufi Order International is at
http://www.sufiorder.orgDances of Universal Peace is at
http://www.dancesofuniversalpeace.org