By far the easiest is to use a Bridge connection for your VM. This makes it look like just any other pc on your LAN, it will be assigned an IP address within your LAN, and it will be able to talk bi-directionally with any pc on the LAN, router included. In this case you can directly forward the port to your VM. You can also make this a permanent arrangement, by reserving this IP address for your VM in your router, so that your VM will always be assigned the same address, and you will never have to configure the port forwarding again.
As you see, in this case the solution does not depend on host OS, NAT vs Bridge, type of Hypervisor ... If instead you do not want to use a bridged connection (thus you fall back onto a NAT conenction), the exact procedure to use will depend on these details....
Can you change the adapter to bridged? That way your VM sits in the local network like your host. What virtualization software are you using? – slhck – 2014-07-07T14:26:28.077
Which Hypervisor are you using? VirtualBox, VMWare, KVM, HyperV, ...? And which network mode are you using? NAT or Bridged? And what is the host OS? – MariusMatutiae – 2014-07-07T15:03:46.230