This is something every company, big or small, should participate in. Whether you meet in an office building or somewhere else, just getting everyone together is the important thing.
First, set a date and time, and give everyone advance notice if preparation is needed.
Having an agenda is very important for these meetings. They don’t happen a lot so you can’t afford to be running around in circles with a group of people staring at you. Prepare a list of topics that need to be discussed: ideas for improvements or suggestions for change, or things that need to be fixed.
Have each person or each department bring a list of improvement or ideas for the future. This is the best time to do that. You want to take advantage of having everyone together to get feedback from employees. Let everyone have a chance to speak and express their ideas whether it is in open discussion or giving each person the floor one-by-one. This is a good time to set goals for the company: monthly and yearly.
This should be done on some kind of regular basis, maybe once a month. Decide how best to run the meeting based on your company size, number of departments, and topics being discussed.
Another good idea, is to have food provided. That always gives people an incentive.