The most important thing is to ensure is that your wheels are not hanging.  The suspension should be compressed so the control arms, etc. are at the same position they would be if the vehicle were sitting at ride height.  This can be done by using ramps, a drive on lift, or simply loading the wheels if the vehicle is on jack stands or a two point lift.  If this is not done the arc that the bar and suspension moves through due to the excessive travel can make things very difficult to line up.