My most productive use of LLMs has been to stub out individual methods and have them fill in the implementations. I use a prompt like:

  public T MyMethod<T>(/*args*/) /*type constraints*/
  {
    //TODO: Implement this method using the following requirements:
    //1 ...
    //2 ...
    //...
  }

Anything beyond this and I can't keep track of which rabbit is doing what anymore.