I would do my research about the client, their brand, the aim of the video and look at any existing material online that would inspire me before undertaking this task. If a voiceover track was supplied I would then use that as the basis of my animation and begin creating to the narration. Some preliminary planning would take place, such as the general creative vision of the piece and perhaps storyboard some of the main parts of the sequence. If there was no voiceover track then I would proceed the same way but perhaps with a music track picked out so I have some audio cues to stick to.