What has helped us a lot is the use of switches that provide a port isolation feature of some sort. Vendors have many names for this functionality port based VLANs, asymmetric VLANs, L2 isolation, etc. but the key point is that the LAN ports to which PCs are connected are prevented from communicating with each other, but some ports can be set to exchange packets with any other port - these are used for servers, printers, internet links. Nowadays one can get suitable switches at around £80 ext VAT (24-port).
When wireless APs are used that support a "client isolation" feature, plugged into an isolated port on the switch, all client-to-client comms are blocked.