Physically most of our college classrooms are setup with the factory model. Students are sitting in rows.
In a room like this, the desks can be moved. In this case you can easily ask students to move their desks into small groups of size two to four. One suggestion, if possible, is to arrange it so that it is easy for you to walk through the classroom. Creating a boulevard in the middle allows you to walk down the boulevard and get to all the groups (e.g. ask the first two rows, and last two rows to move together) .
If your room has fixed desks, all is not lost. You have to ask students to work with neighboring students and get them to turn their bodies at face on another. It's not ideal, but it works.
Don't be shy about moving people. This is part of IBL instruction -- move students to where they will be successful! It is better to be mildly intrusive than to allow other factors to inhibit learning.
Non-physical caveat: The buildings, setting up groups, desks, these are all physical and can assist with developing a healthy, productive learning environment. By themselves they are not sufficient of course. Instructor skill, leadership, facilitation, and coaching are major drivers and can overcome almost any physical boundaries.
Ideally we would have small tables in one part of the room for small group work, and chairs in another part of the room for whole-group discussions and presentations. I hope that future buildings are designed for class discussions, collaboration in small groups, as well as some private space for those times when students need to think by themselves. This is doable and low cost.