The Temporal Contiguity Principle states that people learn best when corresponding words and visuals are presented together, instead of in consecutive order.
Putting the Temporal Contiguity Principle into practice:
When presenting new information, the visuals should be occurring simultaneously with the audio. This is preferred to having one first and the other second, such as an audio explanation first then a visual or animation showing the process, or the visual/animation appearing, then a voiceover narration explaining what was just seen. Ideally the voiceover or narration is played as the visuals/animations are shown in real time.