We had a discussion in my coven about what shamanism meant to individual members, so I will share some things from that: "To me shaman is a person of knowledge, this is a self realized person on a personal path to fulfillment, in whatever form or fashion that is". "To me the shaman (and I don't know a whole lot about them) is the person who is connected with the self and the land, and therefore its people". "To me, a shaman is a person on a spiritual path seeking knowledge and an awareness of the world around them. A shaman is an intermediary between the spiritual world and the physical world, serving to commune with and help both spirits and people. The shaman is in tune with the land, the spirits of the land, the animals, the herbs, etc. The shaman seeks balance in life and in practice". "In my eyes a shaman is a walker between worlds. They stand with one foot in the spirit world and one foot in the human world; this means that they serve as a bridge between the two worlds and of those whom inhabit those two worlds".
Shamanism isn't a practice that is limited to a single culture or practice. Many, many different cultures have shamanistic practices and therefore there are different ways it is practiced, no specific rules unless you follow a specific branch, etc.
For instance, I am a Northern Tradition shaman: this means I work with the Norse pantheon and follow a type of shamanism that incorporates a lot of Norse culture and tradition into it. In this branch of shamanism, communining with the Gods (Odin, Loki, Thor, Freyr, etc) is important. It focuses on learning to commune and honor the landvaettir (land spirits), Dis (familiar wights), as well as ancestors. It incorporates practices such as projection (pathwalking and journeying), trancework, altered states of consciousness, etc.
I think the first thing you should do is figure out if there's a specific branch of type of shamanism you're interested in.