One technique to increase conversation rates is to set a custom thumbnail on your video.
In the examples below, I have created a thumbnail that includes myself and the word Click to Play on it.
Thrive Architect displays a play button on top of the thumbnail. You can choose from multiple icons and set the color for each video.
Ideally you want to choose a color that is contrasting. If you want, you could possibly A/B test different icons and colors using Thrive Leads or Thrive Optimize.
There are 10 icons to choose from, but i think the first one (a youtube button) and the last 6 are probably the best one to use.
There are more examples of animated thumbnails in this post, but here are the icons available for a static thumbnail with some different colors: