This achievement is reasonably straight forward. Collect every bit of money and loot that you can. It is greatly aided by the vision upgrade which lets you see key objects and spot those little bits of loot hidden in corners, drawers, secret rooms, etc.
Emily's pull upgrade which lets her grab objects from a distance can help with this, particularly if you're focused on a stealth run. This achievement is almost certainly easier to get in a non-stealth kill everything in your path run, since it allows you to search for loot more leisurely.
The achievement will unlock the moment you get 60% (presumably by value); it unlocked for me about midway through the 7th chapter, when I'd been fairly thoroughly getting maybe 90% per chapter up to that point.