When we first started Daily 5 and were moving from GR to strategy groups, we held on to our groups based on Guided Reading levels. I think that’s a great place to start. As a teacher, you feel comfortable with the GR groups, and can introduce your students to the format of Daily 5 to replace what you might have spent your time as “centers”.
That’s where we started. As we got more involved with Daily 5 and CAFE, we “almost intuitively” moved toward the strategy group/conferring model. I’m thinking of our first grade teachers who rely almost exclusively on their individual conferring, with strategy groups as a back-up.