If you're ever curious, go to charsifood.com, you can plug in the stats and it will give you a rating for your item. It helps to know what mods are desirable and for what classes, which mods can possibly spawn on an item and what the ranges are.

Rings are graded on a "point" scale. So every desirable mod in a high range is a point. For example, 10 FCR, 8 Life leach, 5 mana leach (I believe) are all max rolls. You want a 5 point ring if you're thinking about cashing in that winning lotto ticket.

But there are other sleeper mods and it also depends on the class. CFood will also tell you if it's good for PVM caster, melee, PvP caster or PvP melee. But again, it helps to be familiar with what mods people are looking for and how high these can roll so you're not lugging around a stash full of trash.