I've never been to keenest of audience when it comes to ice dancing as i have poor discrimnatory power for the teams. Most look similar. From what I can catch from commentaries:
1) Speed, of course the faster the better
2) Skating in opposite directions is more difficult
3) Doing steps separately is more difficult than doing it holding each other esp for coordination
Some are more obvious like with Annisina and Peizerat where she lifts him instead of the other way round.
What are the other things to look for? Sometimes the little nuances make watching it far mroe interesting. Need some fodder for my Worlds watching in Dortmund.