This is all a part of the conditioning process and for the most part it's not about how you keep you birds just before a show, it's how you keep them 100% of the time. A bird that has been kept in a tiny little pen will not have the same conditioning as a bird in a larger pen where it can exercise and develop muscle condition. Fresh food, water, a clean environment, a pen that is a reasonable size with roosts if possible and good quality feed. I also make sure my birds get natural light. I absolutely will not keep my birds in dark, dingy pens like I've seen WAY too often. I designed my coop so that all my pens will have a window in them. I also like to free range my birds when I can....they love it and pick up extra nutrients that the feed may be missing. Only do this though of your area is safe from wandering dogs and other predators.
A healthy happy birds will have glossy feathers that grow at a reasonable pace. I tend to feed my show birds a lot of 'grower' feed as opposed to 'layer' which is what we get up here in Canada in my area.
Urban Coyote