A bigger issue seems to be the prevailing assumption that being a Captain is the same as being an FO, just that you get to taxi the airplane and sign the release in one extra place. Some enter training woefully underprepared for making command decisions. As a result the training department has put together a command leadership class to help bridge the gap. If you want to upgrade you need to get started long before that though. Spend some time talking to Captains, especially the senior ones. Ask them to show you the process they go through when looking at the release/AML, etc etc. Look at the release yourself and start figuring out how to determine if you can operate this flight safely and legally with what you have. Start thinking and caring about fuel loads and planning etc etc etc. Imagine yourself faced with various abnormal/emergency situations and think about how you would handle them. If you're not sure, start soliciting advice from multiple captains to get a feel for what they think. Research the manuals to see if there is guidance in there. It isn't rocket science, but it does take thought and preparation.