get a handle on something

“I always liked making lists and trying to get a handle on something that interests me.”

To really get a handle on something resembling moderation, try an approach espoused by organizations ranging from the American Heart Association to Sesame Street: Think about food in terms of "everyday" foods and "sometimes" foods.

Likewise, to get a handle on something like global warming, we try to mentally simulate a warmer environment in the future.