Many scholars have attempted to provide comprehensive yet concise descriptions of what is common to all religions. I think that Huston Smith, a Doctor of Religious Studies, has best summarized the features of religion without some sort of bias or favoritism towards a particular tradition. He describes these features as the following:
First, religion offers explanations. Who are we? Why are we here? What do we do now? Religion seeks to answer big questions like this as well as questions about more minute aspects of life. Religious explanations often cover topics like eschatology—what happens after death or at the "end of the world"—and cosmology—how the world (or universe) is organized and how it came to be.
Second, there is a sense of mystery in religion. Some faiths explicitly address the sense of mystery (as in Catholicism) while others may be more subtle (as in Buddhism.) As humans, our experiences and understandings are finite by the very nature of what it is to be a human being. Religion is empowering for many in that it transcends the finite boundaries of human experience and offers a means for negotiating that which we cannot know.
Often times this negotiation occurs by way of ritual—the third feature of religion. Rituals are prescribed, repeated behaviors with desired and intended outcomes. Ritual and habit are somewhat similar in that they are repeated behaviors which offer a sense of comfort. Where ritual differs from habit is that ritual is understood to be in accordance with some supernatural force and it is carried out with specific intentions.
Ritual can give way to tradition, and may even transform through tradition. For example, the Christian baptism stems from the Jewish mikveh. The mikveh is used for ritual immersion (or bathing) in order to be spiritually pure. When Jesus Christ was baptized, he was undergoing a form of mikveh initiating him into the Priesthood. Today, most Christians are baptized to initiate them into the faith either by immersion or a sprinkling of holy water. Notice how this tradition began with total bodily immersion and an intent of marking someone as spiritually pure and has since transformed into only requiring a sprinkling of water to mark someone as of a particular spiritual identity.
All religions have a sense that there is a right way to live and act, and if we do this, we reap some sort of spiritual benefit. In Christianity, this is often called grace, and this is the term Smith uses. However, I feel using the term "grace" is Christo-centric and seems to exclude religions which do not employ a concept of God. Some other examples of "being right with all that is" would be the concept of dao in Daoism (Taoism) and kamma (or Karma) in Buddhism.
Finally, all religions have a sense of authority in regards to religious matters. In some cases, the people with religious authority are priests who undergo years of training and education to fulfill their role. In other faiths, emphasis is placed on an internal authority and personal understanding of how to live in the world.