You will have to see what works best on your cat. A bath the day before the show may be just the ticket. On the other hand, yours may need to be bathed four or five days ahead and allowed time to fluff or sleek up. What shampoo to use varies also. Some coats react differently to different ingredients.
Many owners follow their cat's bath with a flea dip to help keep fleas away for a few days.
Be careful in using flea products. If you use a flea shampoo, do not follow it with a dip. If you use a plain shampoo, you may follow with a dip, but be sure the product is meant for cats and be sure to use proper dilution. You can make a cat sick by careless use of flea products. This is fine, but be sure to comb the extra out - the judge will not be pleased if the cat brings a cloud of powder along with it.