FISM Champions like Lance Burton, Richard Ross, and even Shimada all were known to practice a single effect for YEARS before placing it into their repertoire... I'm not saying "Show" or "Act" but rather referring to that collection of material they know like the back of their own hands for those "just in case" moments i.e. pet effects & routines.
Lance's Dove Act that won him the Grand Prix was the result of over ten years of practice... the practice came in the form of live performances at various amusement parks across the country where he presented the same exact act day after day five to eight times a day for years.
Richard Ross' Linking Rings routine is something he honed for over three years before performing it... and this is a guy that was coached by Fred Kapps and another FISM favorite, Peter Pit.
As has been said, it takes as long as it takes but you have to be careful not to allow that to be a crutch. Far too many people collect material, play with it and never do anything with it. Too many cling to a "dream" concept and keep making excuses of
"I have to get this, this and this piece first before I'm ready..." rather than step out and gently build. I can assure you there is no act in existence that is remotely close to where the original vision started... that's just how it works in reality. It's just like playing Dungeon & Dragons... the role of the die changes everything you had planned for your character.
So the rule is, you do have to jump into the water in order to learn how to swim... working a live audience (other than family & friends) will teach you all those little things you don't find mentioned very often in the books or lectures (the books & lectures that do mention them tend to not sell very well for some odd reason

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So the process is simple; when you feel competent enough with your material, try it out on some folks. As you do so try to pay attention to their reactions in conjunction to what you are doing... keep notes and review them daily as you walk through each routine and see where you can tighten things up... getting rid of bits that don't seem to work or else looking at ways of improving the parts that are weak and so forth. Just as play writes break in a show "off Broadway" that's what you'll be doing; trial runs to get the bugs worked out. You'll know that you're "good enough" when people start offering you gigs and offering to pay you more than you may think you're worth just yet... and those that don't want to pay you, don't get the show... that's a very hard lesson to learn and put into practice but it is an important one -- there's always an exchange!
Get critique from laymen as well as other
performers (not the guys from the local magic drinking society but actual working pros) As you cultivate things get with people that understand theater, ask their help in choreographing the act, figuring out the proper outfit to wear, lighting, music, etc. All of these things are the accents that transform your hard work into something enchanting.
