Cisco admin to optimise and secure a network

I am running a network with Cisco 2811 router connected to 3 catalyst 2960 switch I don't have much knowledge in Cisco cli so I would need someone's assitance in making few small modifications I would like to optimise and secure the local network by various mathod - block untrusted dchp server from the lan enable qos disable various usages of applications (file sharing p2p) secure network so anyone on lan cannot get any information or connect to the router. Any other recommendation for securing this public network will be very useful.