Start with free practice
Many AI assistants are available for free - this is enough to master the main thing: how to pose a task in words. Open any one and start giving real tasks. Practice is more important than paid courses at the start.
Learn from your real-life problems
Don't look for abstract exercises - take your cases and solve them with AI. This way the skill is immediately useful and is better remembered. The free and most effective practice is your own work.
Take structure, not chaos
There are a lot of free materials, but without order they provide little. Stick to the basics (prompting principles change slowly), choose a couple of reliable sources, and learn for a specific task, not for future use.
Bring it to fruition
Free training fails when everything is abandoned halfway. Set small, specific goals and follow through. One completed skill is worth more than ten courses started.