Make a 'recce' visit first...

Your first visit should be simply to familiarize yourself with the way an auction works. You may be surprised at the volume of cars on offer and the speed at which they are sold. It can be quite unnerving at first, but after a while you'll get the hang of it. Take a notebook with you, or better still get hold of a catalogue of the cars on offer; many auction produce these on the day of the sale. Take notes as the cars are driven through the auction ring, particularly of the prices the cars are achieving, that way you'll know how far your budget will stretch.