A clear desk policy. Establish that whenever people are out of the office for more than a certain time - say 1 hour - they must clear everything from the desk. Having a locker to put things in is essential for this.
Well organised team storage. Piles of files can't be left on desks - but shutting them away in lockers can be worse. It will actually increase efficiency to accept the discipline of returning files to team storage and making them accessible to all.
Shared libraries of reference materials have the benefit of reducing duplication and preventing personal silos of information.
Have the same agreed compendium of essential information at each desk and/or online. E.g. key dates, fire escape routes, important telephone numbers, etc. And ban the maverick pinning up of "essential" information by desks to prevent "professional personalisation" of desks.
Create a beautiful environment! Provide attractive pictures, planting, water features, etc and this will justify the restriction on people putting their own knickknacks on their favourite desk.
Ergonomic work positions. Getting in the best and ergonomic workplace layout will help people accept working in different positions. Chairs must be adjustable - or some will claim they have to sit in a certain place each day.
Laptops are preferable to desktop PCs. That is because they can move everywhere with one member of staff, and any specialist software installed moves with them. This will prevent people laying claim to one particular space for IT reasons and enable more effective flexibility. When working in one position with a laptop for a long time, a keyboard and mouse, laptop stand and/or additional screen should be used.
Provide ample touch-down space to cope with peak demand. That is, places where people can connect their laptops to work for short periods. These can be touchdown bars, or locations in resource areas, informal meeting/refreshment areas etc.
Work in non-exclusive team areas with fuzzy boundaries. It's good to keep the team connection and work with each other to share space effectively. But space sharing will not achieve the maximum benefits if teams become exclusive. The aim should be to break down barriers, and encourage working across teams. "Qualified Flexible Team Space", we could call it.
Have a good telephony solution. People need to be able to log in to their extension whether in the office or out, and from whichever desk they sit at.
Encourage flexible working in practice. People working from home and on the move, and working compressed working weeks in particular will reduce the daily demand for space.