Remove all loose skins but try not to overskin as this spoils the colour. All classes of shallots are dressed. Tops folded over and bound with plain raffia. Damp the raffia and damp the tops by wrapping them in damp kitchen paper for a few minutes. This stops the skin on the tops cracking.
Usually classes are either
Exibition Shallots, which are as big as you have but matching bulbs with good shape and colour are more important than size.
or
Pickling Shallots, not bigger than 30mm. Condition and uniformity are again important.
At the show place them on fine dry sand. Plastic flowerpot saucers are good, 7 inch size for exhibition, 5 inch size for pickling. Pour in the sand to form a mound. Put a nice bold shallot in the middle then place the others round it. Smaller towards the front, that is unless they all match perfectly.