There are so many things that can be done by a network administrator to improve network (LAN) performance. I will try and list some from my own experience:
1. Replace all hubs with switches; A Hub is known to be a single collision domain and floods every frame it receives out all interfaces. It’s up to the computer to select which packet has its MAC address in the header and discard the rest. In turn, switches separate collision domains and use MAC tables to intelligently forward frames to the destination MAC address.
2. Watch out for loops! Loops in switched networks cause broadcast storms on the network, multiple frame copies which eventually slows down the network and increases the switch CPU utilization. Some techniques used to prevent loops on the network include; CISCO's STP, Extreme Networks's EAPS.
3. Loose connections; lose connections cause switch ports to keep flapping, this increases network messages being exchange across end points and hence cannibalizing on the bandwidth intended to carry data. Loose connections are caused by bad cable termination and bad patch cords.
4. Use interfaces with enough capacity at the uplinks; uplinks are the interfaces interconnecting switches to other switches or switches to routers. Make sure that there are no bottle necks at the uplinks. For example gigabit interfaces for large networks and 100mbps interfaces for small networks.
5. Watch out for computers with viruses on the network. A computer virus will always try to spread over the network and will always be sending unnecessary messages over the network which will clog up your bandwidth. Maintain a virus free network by using a good anti-virus with latest updates.