Wash them about a week before the show. I typically use baby shampoo. Others use dog or horse shampoo. White vinegar helps rinse out suds and also helps remove stains. I have been told that Cowboy Magic greenspot remover is good on stains; I haven't been able to find it, so haven't tried it myself.
After the bath, while they are wrapped in a towel is a good time to trim toenails and beaks. Finger or toenail clippers work fine. Be careful not to cut into the quicks.
VetRx or body oil on comb and wattles, legs, spurs and toenails--just a bit to shine them up.
Glycerin in the rinse water will give shine to hard feathered birds, as will Pinks (a ahir styling product), but don't use either on silkies--tends to weigh down their fluffiness, making their feathers look stringy.