To find out God's will, ask God for his will. You do this by praying to God, which is simply addressing God, in this case with a question. You then sit quietly and take note of what comes to mind. What comes to mind may be from God or it may not, but you have to trust that what comes after praying for God's will is more likely, on average, to be God's will, than if one had not prayed.
Here are some other ways of testing what comes.
(1) Run the idea past trusted advisors whose lives demonstrate usefulness, cheerfulness, and kindness.
(2) Ask: is the idea for the good of all?
(3) What are your motives? Are they selfish?
(4) Have you any experience of the idea in question? How did it work out last time?
(5) What is the cost of the idea: what would you do instead?
(6) Will this bring short-term gain or long-term gain? Will this bring short-term discomfort? Will this bring long-term discomfort?
(7) Are you following a principle (which allows for the application of and trade-off with other principles and adjustment to situation and circumstances) or a rule? (Tip: principles are more reliable than rules).