A simple tip for improving the results you get from your harness: set a goal.
Describe what you want to achieve and how you will check the result. Anthropic's prompting guidance also starts with defining success criteria.
If you are not sure how to set a goal, or even what goal to set, just ask the AI. Have it prepare a prompt and goal for a new session.
For example:
Start a new session to create a video about "X". Create the prompt and goal for that session.
Read what it gives you. Does the goal match what you want? Change it if it doesn't. You can learn from how it turns your vague idea into something you can work towards.