so basically it goes like this:
modprobe kvm-intel
modprobe tun
ifconfig eth0 0.0.0.0
brctl addbr br0
brctl addif br0 eth0
ifconfig br0 0.0.0.0
dhcpcd br0
#######################
then create your qemu-ifup script with this content:

#!/bin/sh
echo "Executing /etc/qemu-ifup"
echo "Bringing up $1 for bridged mode..."
/sbin/ifconfig $1 0.0.0.0 promisc up
echo "Adding $1 to br0..."
sudo /usr/sbin/brctl addif br0 $1
sleep 2
######################################
Now use this a base command to start your VM up:
qemu-system-x86_64 -net nic,vlan=0,model=ne2k_pci,macaddr=00:00:00:33:22:11 -net tap,vlan=0,ifname=tap0,script=qemu-ifup -hda vdisk-slack12.img -m 400