There are many strategies for developing decision making - this may take the form of engaging in activities which involve fact vs. opinion, debate and discussion of positions on current event topics, persuasive writing and speaking, science fiction and scenario building (for example, Future Problem Solver program below), and even conclusions about bad designs (here).
Currently with our kids we're enjoying the old Sidney B. Carroll book You Be the Judge. This little book provides short summaries on court cases, and asks readers make decisions on how verdicts should be made. An example: A man and a pregnant woman are on the street when a tornado hits - they knock on a door to be let in, but the homeowner won't let them in. They get hurt in the tornado - do they have a right to demand that that homeowner pay some of their doctors' bills? (BTW: Based on reasoning from another court case, Carroll suggests that the couple have a reasonable chance of winning).
Decision-Making Lessons Biology
Future Problem Solvers
Decisionmaking Course Notes