For the first half of Age I you should be focusing on setting up your engines using what is readily available from the card row. Iron, Science, Civil/Military actions should be on your priorities. Setting up your military early is a bit of a gamble since you will be using your military actions for some turns to build and won’t be drawing military cards then. If you’re able to get more Military actions then you improve your chance to get the right cards to punish your opponents before they can catch-up.
Past the half point of the first Age, you have to start thinking about patching holes. Age II is approaching and you will be loosing 2 yellow tokens. Are you still producing only 2 foods? Are you behind on military? Will you be able to play a technology at least once every 2-3 turns in Age II?
How will you produce more rocks? And what about Culture…?
When you understand your weak point you can easily decide to sacrifice 3 civil actions to get the card you absolutely need to get things moving forward. If you are not asking those questions before you hit a wall you will be relying too much on your card row luck and might loose a few turns until you get the right card.
On the subject of corruption, it really should be avoided at all cost for the first 2 Ages. Take the time to try different set of actions using the undo option. Also, if you’re not sure about building a 4th or 5th mine/farm, you might be better off investing for science or culture since you never have too much of that.