This is the question I've been asked constantly. So I think this might be a good topic to talk about for 2nd week.
Before we start it, I should make myself clear, there is NO magic trick can double up speed, or "appeal" button to magically turn animation to master piece (If there is one day human ever invent this function, then we all gonna lose job for sure.). Everything comes from practice, sounds cliche? but it's true. Getting more experience is the only one way, which might include the detail observation from real life, knowledge of software or most of time, we learn from our mistake. So, don't be afraid to experiment new workflow, or try a new way to approach a shot. The more different attempt we had, the more experience we got. As a student, I think the priority is to learn how to make it right but fast. We can only produce quality animation with speed when we already knew how.
Back to the topic, even though there is no shortcut to double our speed, there are tools can help . I'm going to introduce the tool I use the most while animating, "TweenMachine". (you can find it at CreativeCrash.com, registration needed)
How to use: select controllers, move timeline between 2 keys, and move the bar (can't be easier.) -100% means the new key will be exactly like pose A, and 100% will be pose B. You can turn on the "overshoot" under options menu, which allows you pull the bar to 150% or -150%.
Here is a jumping demo I made to show how it works.
Screen Left, no breakdown, key poses only.
Screen right, this took me around 10 minutes to add breakdown poses by only use TweenMachine (further Adjustment needed), the red dot on the right bottom corner means breakdown poses.
You can download this video from HERE.
So I use TweenMachine to quickly create breakdown poses, and also decide the pose favoring. For example, I want the head lead the jumping, so the head will be favoring key pose on F15, and hands are delayed to create follow throw. Same steps applied with landing, the body come first, and then head and hands follow.
In sum, even though by using this tool, you can quickly get the favoring breakdown, adjustment still needed for the final pose. It can quickly gives you a starting pose, and avoiding the wicked curves cause by gimbal lock.
P.S. you can do the same thing without using TweenMachine by borrowing keys on timeline, by that means, move your mouse one the place you'd like to borrow between 2 poses, middle mouse drag to middle and set key.
Hope this helps, if you know something works better, please kindly share with me. :)
Cheers!