When I begin to animate, the first thing I tend to do is analyse references from other work in games or movies that achieved what I am trying to accomplish. In the example below, I could only use video games as a reference, and began drawing up a story board noting the particular actions and movements the hands make when they reload. I then framed out my general actions with stepped curves and began to get an idea of how the animation was going to look. The combination of these actions in pre-production takes the most time out of all my steps, but are important in determining whether or not I may have to fix it to look better down the line.
2. Second Pass and In-between's
The next step I take is to add to my key frames by creating more in-betweens to begin showing secondary action, follow through/overlap, and various other animation principles. I like to think of it as putting little visual notes on where and when I need to iterate on specific motions or to change the timing between frames. This stage is also where I tend to begin to refine any secondary action. In this case, the cylinder was coming out too early so I changed the timing to have it come out a little later. New frames were added to the fingers as well.
3. Final Pass and General polish
Now that most of the animation is finished, I changed most of my curves to auto or spline in order to make the overall animation look smoother while fixing any timing issues that came up as a result. Most of the little notes I made in the previous pass I now act upon and emphasize those principles, like adding overlap on the right hand after swinging down, or the left bending upwards upon going down. This is also the phase where I add any miscellaneous features to the animation to sell it better, the bullets falling out of the chamber being one such feature. I usually discuss with superiors and peers about what I can do to improve the piece, regardless of whether or not they're animation experts (sometimes outside help is just what one needs). At this stage, consulting with others is critical, as the piece is almost finished, and any large changes needed must be addressed.
4. Lighting Pass and Additional Asset Production
Finally, with the piece essentially finished, I begin to add light to accentuate the animation and render it out. I like to use Maya's default rendering hardware, but I can use other programs as well. Here, I will also add extra assets that make the piece look better. In this bit, I added a target and background. The target bounces back and forth after being shot, which adds little to the overall animation, but makes it more aesthetically pleasing to watch, even if only a little. Despite how fast this pass can be done, it's just as important as previous passes. While animation is what the main focus of this piece is, making it look like it belongs in a scene with a nice colour pallet will get more people looking, which is the goal.