Creating a new image
$ qemu-img create -f qcow2 image.img 20G
Bridged networking
This is what I did to set up bridged networking for my KVM guests:
# vim /etc/network/interfaces
And set my wired interface to manual
and define a bridge interface
br0
which my KVM guests will use.
iface eth0 inet manual
post-up ifup br0
iface br0 inet dhcp
bridge_ports eth0
Starting the KVM guest
Starting the KVM guest by booting from its CDROM using the Debian stable ISO as the CD:
# kvm -net nic,macaddr=00:00:00:00:00:04 \
-net tap \
-cdrom /home/torstein/tmp/debian-8.1.0-amd64-netinst.iso \
-boot d
-m 1024 \
/home/torstein/virtual/wind.img