Subjugate Lots of Titans
Subjugating Titans is one of the main things, if not the main thing, you’ll find yourself doing in Attack on Titan. But you only have to slay the ones you’re told to in order to complete a mission, which often times means only slaying a handful. Yes, there are some missions that will make you kill everything on your map, but those are pretty rare.
If you want regiment funds, you’re going to have to go out of your way to slay even more Titans during a mission. Don’t worry, though, if you’re going for an S-Rank this will actually help you, not hinder you. While time is definitely a factor in your overall mission rating, the amount of subjugated Titans is a less lenient parameter. You usually have more than enough time to get everything done within any time limit.