HP 2824 - Proper Way To Setup Additional Subnet?

We've never had to do this before: best practice on setting up an additional subnet on a physical network?

For example, main network is 10.1.1.1, we need to setup an additional 10.1.2.1 to support more devices. We need both subnets to see each other and the servers on 10.1.1.1. We also need the new subnet to have access to the internet.Equipment we have: HP 2824's (2 current VLAN's - second one is for phones) and Untangle for our firewall.