I think what's really important, and concomitantly complex, is efficient rehearsal, by which I mean the repeated execution of a routine or full show as if to an audience. By comparison, practice of purely mechanical actions, such as sleights or flourishes, is relatively straight-forward. There are factory workers all over the world who achieve almost super-human mastery of manual tasks simply by virtue of repetition, even without a particular desire to improve. So, on that basis, and with some additional reading in expertise studies, my advice for efficient practice (assuming mastery is your goal) would simply be this three point plan:
1. Ensure you learn the technique from a reputable source so that you completely understand what you're aiming for.
2. When you're sure you understand what your hands need to do, execute that technique 10,000 times.
3. Congratulations, you have mastered that technique.
It's pretty much as simple as that, although there are a few supplementary notes:
1. A repetition of the technique can be as slow as you like, speed will come naturally with time. The important thing is to execute the move with what I'd call a "tolerable level of success", otherwise it doesn't count towards your 10,000 or you're basically just practising doing it wrong.
2. This "tolerable level of success" will vary from move to move, and is therefore down to your own discretion, but I'd recommend being relatively harsh with yourself. For example, I'd count dropping cards as a fail for any move, but maybe you'd be lenient enough to allow shuffles to be slightly imperfect weaves.
3. Break techniques down into as many variations as you can think of and count each one of those as a separate move requiring 10,000 repetitions to achieve mastery. Taking a classic pass as an example, you might want to count "Classic Pass when Selection is Returned to Lower Half of the Deck", "Classic Pass in Context of Card Table Procedure", and "Classic Pass after Holding Pinky Break" as different moves, needing to be practised separately. Of course, the practice of each of these will inform the other, but you won't end up with the problem of how you get into and out of moves because you'll have mastered them for all required contexts.
4. Don't just take my word for it. Read The Cambridge Handbook of Expertise and Expert Performance and then try and keep reasonably up-to-date with expertise studies. It's a fairly new field of study, so I wouldn't be surprised if there are new developments that would give a more precise framework for practicing magic.
Hope that's helpful.