I take your post at face value, as a genuine search for improved command preparation material. The best material available is right between your own ears, and this advice.
Every captain you fly with will demonstrate good and bad examples of his craft. One of your essential tasks is to recognize the difference. For your own standards, follow the best, and reject the worst, as advised by Sleeve Wing. Every generation of new captains should be better by following this advice, far better than learning by your own mistakes.
It is difficult to appear like captain material when you are sitting in the right seat. Part of your preparation can include bolstering your own ego a little, and your image with your captains, flight engineers, and others. Here are some things you could be aiming for every day:
Feel like a captain
Think like a captain
When you are PF, make decisions like a captain
Fly like a captain
Perfect checklist reading
Perfect actions
Perfect responses
Perfect normal procedures
Make sure everything is rosy at home. Let your closest friends and / or family know that you are working towards your goal. Take your partner out to dinner, and explain the temporary pre-occupation with your ego and
PR for the upgrade.
It won’t hurt your prospects if you aim for self improvement. Your confidence, attitude and ability will not go unnoticed.
Of course it’s not all just
PR, is it? It’s a new you.