Use language and a style of delivery that is consistent with the programme content
The role of audio description is simply to convey information. It should not add to or detract from the feel or atmosphere of the programme. A description that is radically different in language from the programme content or that uses an inappropriate tone can destroy the feel.
Directions and techniques
Use language consistent with the nature of the programme
Use terminology, idioms, etc. That match the programme content. Otherwise the description may well disrupt the feel or atmosphere and unnecessarily draw attention to itself.
Make the delivery fit the nature of the programme
In a tense thriller or drama, the delivery should be steady and where the background music is menacing, the voice should reflect the tension, without becoming melodramatic. In comedy, the narration should also be steady but can be delivered with a slight smile in the voice, but never laughter.