It's been pretty ad hoc, but my prompts are nothing special. Things I generally do:

1. Top end model on high/xhigh thinking (last time I did it it was Sol xhigh I think)

2. Make sure it creates some representative fixtures of different sizes and sets up a good testing, profiling and benchmarking loop that doesn't require my input.

3. Make sure it has access to reference implementation code

Edit: Oh and one obvious pitfall that for some reason I still have to remind even smart models of from time to time: make sure it knows not to try to parallelize its benchmark runs. I've occasionally had an agent struggle to figure out absolutely nonsensical data because it tried to run multiple tests on the same compute hardware simultaneously.