A good place to start are the super cheep, transparent plastic locks. Keep in mind these are extremely easy. You will pick them in seconds and get a great confidence boost, but they won’t really help you improve.
You will feel like a super hero, but get bored with these within 20 minutes.
Once you get bored with the toy locks, try these training sets for intermediate lock pickers:
The last two items on the list are a must have if you want to fully understand counter-rotation.
Some real life locks to use for practice: