I like the liquid pre-soak products for minimum-trouble prep that doesn't usually leave an oilslick. When you tie or buy dry flies, put them in the jar, close lid, turn it upside down for 20 minutes or so. Dry the flies on a paper towel; Box 'em, fish 'em. Powders are for drying a watersoaked dry fly during use.
When a dry fly starts sinking, swishing it underwater, then drying it by falsecasting seems to bring it most of the way back.