The short version is, it's very vague; Magic in SR is veeery perception-based, like the UMT indicates. I mean, magic is a manifestation of the mental structure of the user, and the effects of their magic strongly reflect that. So... I guess the answer is, the ritual is whatever is most appropriate to him.

Hermetics are typically "logical" spellcasters - using formulas and spellbooks, instead of intuition. Symbolism becomes very important, as does structure.
For example, you could have a single circle, used to contain the spirit until the spell is complete. You could have TWO circles, one to hold the spirit, and an outer one surrounding it that also holds you, but keeps the world out. The spirit could be in the center of a pentagram or a star of david. You could have four candles (reflecting the four elements), five or six (the points of a star), or none. Maybe to summon a spirit of fire (fire elemental), the whole thing is centered around a bonfire, or maybe a single burning coal that's brought to life. For an air elemental, maybe it has to be under the air. Maybe it involves lots of burning insense; maybe it involves musical instruments, or maybe he's a spell of binding from a book...
It's just very vague. It's highly personal to the summoner, their "school" of magic, and their personality.