wow, only a week for sybil. i do sybil for 2 months now and i'm still so slow...
anyway, the only way to practice is just to try over and over and repeat that step. at the moment, i'm practicing roughly about 10 hours a day, but i still suck. i started only about 4 months ago with flourishing/magic, and so far i am very confident, because i think i have achieved quite alot in a short period of time, but magic and flourishing are arts, and just with most arts it takes years, decades or even your whole lifetime to perfect what you're doing. the most important thing is to keep going and have fun with it.
one more thing i have to say is the following: the longer you handle cards, do magic and flourishes, the easier it gets to learn new techniques, because you have a certain feeling for a deck and that's something you can't lose even if you don't touch playing cards for a month or a year. it takes alot of practice to reach that point though.
so now a quick answer to your questions:
best way to practice: start slow until you get comfortable & secure with the movements, then often the speed comes naturally.
how many hours of practice: that's a question that can't be answered. it depends on alot of factors, some of them being: how long have you been flourishing, what kind of moves do you like, how similar are moves you already can do to the new ones, how hard is the flourish, ......
just as an example, i think i can't do pandora at the moment, because i can't do a tornado cut. of course if i learned pandora, i could also do the tornado, but i prefer learning the basics first (i just don't want to learn brian tudors bad habit, because i hate the cut)