One tricky situation that comes up with descriptive audio is when there is a lot of constant talking, but there is also a lot of visual things happening that is important, so there isn't any space for the descriptive video.

Adding descriptive details in regards to aliens for both physical and environmental/cultural situations. Using a Star Trek reference, you can mention that the Klingons have ridges on their foreheads and wear armour. Visually, we can see they are a very-warlike race is armament, attitude and atmosphere. Whereas if you compare it to the Borg, they are covered in cybernetics, and their ships could be described as highly technologically advanced but lacking any kind of artistic decoration.

Character description profiles: be detailed with descriptions. Even Provide the descriptions outside the series, perhaps an article.