What’s the fastest way to become strong at AI engineering in 90 days?

"I want practical advice from people who have actually built AI systems. If someone wanted to become meaningfully strong at AI engineering in 90 days, what should they study, build, and practice each week? I’m looking for concrete guidance on model APIs, evals, prompting, RAG, agents, debugging, deployment, and how to avoid fake progress. Strong answers should include a step-by-step roadmap and real project ideas."