One thing that helps is to write an AGENTS.md file that encodes the knowledge and tricks you have of the codebase, like running a single test (faster feedback cycles), common coding patterns, examples, etc.

I went full meta and sketched out a file, then had an expensive LLM go through the codebase and write such a file. I don't know if it's any good though, I only really use coding assistants to write unit tests.