As much as possible. Practice has become an ellusive secret in our art. It really has. Everyone looks for the quick "easy to master" fix. They buy a book and ask someone who doesn't even know them, what they should read first. Or how they should "approach" the book. My method is to OPEN IT...and start studying. Anyway, practice will always be what separates the men from the boys in ths business. No excuses.
I couldn't believe that on Lance Burton's Young Magicians special, he actually suggested that its better to practice a little here or there, instead of something more intensive! Did Lance really get where he is today by working on the doves for 5 minutes, then an hour or two later after watching some tv, work with the candles for 5 minutes, and then the next day spend a few minutes thinking up an idea for an illusion? No. We know that Lance worked very hard, and surely practiced a lot, to get to where he is today.
But you love Copperfield. That man never stops. Sure, he's usually practcing or rehearsing bigger things, but the size isn't important. Its the practice and the rehearsal that we are discussing.
Card tricks? My great love. I practice with cards more than anything else. But I couldn't tell you specifically.
Its tough sometimes: Book the shows, do the shows, (and the million and one things that go along with each: Set up, phone calls, letters, travel, etc), and still keep your love in focus. Sometimes, even when I'm working, I'm looking forward to coming home and PRACTICING.
This has been ONE MAN'S OPINION.