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The right way would probably start with not getting three goldfish for a 20g. I'd honestly do 1 fancy max, and mayyyybe 2 if you had excellent filtration and did frequent water changes. Unless you're upgrading them soon?
You've got two choices. Fishless or fish-in cycling. Honestly, unless you have a good amount of seeded media, fishless is probably going to be less work than fish-in with a goldfish. If you really have your heart set on more than one goldfish you'll need a larger tank.
As others have said, there's no fast way to cycle a tank. It takes time, typically 3-8 weeks either way you go (fish in or fishless). Also goldfish are large messy fish and require certain care. One fancy can go into a 20 gal, but no more (you'd need 10 more gallons for each additional fancy, so for 3 you'd need at least a 40 gal tank). If it's a comet, common or koi they belong in ponds. Here are some links for you: Guide to Starting a Freshwater Aquarium - Aquarium Advice http://www.myaquariumclub.com/goldfish-101-11174823.html (written by a member here who is very knowledgeable about goldfish)
Even fancy goldfish get large. In a year my orando's and other fancies went from about 2-1/2 inches to well over 6+ inches. Even one of my 6+ inch fancies would be horribly cramped in a 20g. On your other thread the same issue was addressed. You need to do smaller fish, a small fish community is perfect for a tank this size and there is no issue about fish outgrowing the tank.