I ask myself this same question every day.
Animating for games can be a bit overwhelming at first if you're not familiar with what the differences are with other mediums. As with most things, if you break it down into a workflow that benefits you with focussed steps then it becomes much more manageable.
Here are some of the steps and thoughts I have when tackling this issue.
Firstly, it depends on the player camera position in the game. Even though the player can manipulate the camera position in many games, the default camera position is still seen most commonly. The character should always read well from this position to start with. To get a good representation of what you'll see in game I find it helps to recreate the game camera position (including FOV) as accurately as possible in your animation package.
Next, having a solid understanding of body mechanics should get you a lot of way there with the other angles. As the player can manipulate the camera, you simply can't cheat things as you might do with a fixed camera to get the best readability.
After the first pass is ready it's essential to try it in-engine and see how it reads in the context of the game. Then I'll usually go through the whole animation again to check for readability and push poses through the orthographic camera angles (e.g front, side and top). Trying it again in-engine after making any changes is always the best way to measure readability.
Finally, to cover all your bases get somebody else to play it in-game who hasn't seen it (usually your lead/supervisor/designer) for any notes or feedback.
Do you have any thoughts or questions regarding this topic, or any new questions you'd like to see covered? Drop a comment below!