Let me share some guidelines I use when making decisions. Though I will use the New Testament as a groundwork, most religions and even some agnostics may agree to some of these ideas. Herein I'll discuss the groundwork for making decisions and three types of decisions: day-to-day more trivial decisions, minor but important decisions, and major life-changing decisions, and give some guidelines I follow and the reasoning behind them.
Let us begin with the groundwork. The law of Moses was letter of the law. In Deuteronomy 17:6 and 19:5, we see the letter of a law on determining truth when accusations are made. Jews established truth in the mouth of two or three witnesses. Jesus introduced the spirit of the law, which is broader. The spirit is not easier than the letter. You will find it harder to love your enemies than to love your neighbor and hate your enemy. Consider now the spirit of the law for establishing truth. Paul said to the Corinthians:
This is the third time I am coming to you. In the mouth of two or three witnesses shall every word be established. (2 Corinthians 13:1)Many of you have heard this before, in various contexts. Let me introduce one context many have not considered. You have two witnesses inside yourself. They help you establish the word within yourself and what actions you should take. The two witnesses are your heart (emotion and feeling) and your mind (logic). The Greeks understood this idea long before the Christian era. The words they used were not 'mind' and 'heart', but 'pathos' and 'logos', or roughly translated, emotion and logic.
Now that I have introduced the two witnesses within you, I will discuss how to use them for the three decision types: trivial, minor, and major. Trivial decisions are the easiest. If you believe in a God, you likely believe He gave you the right to choose. Most of these decisions probably don't matter. What you have for breakfast probably doesn't matter too much. You probably don't need divine guidance for trivial things. Make trivial decisions on your own. Decide what your heart desires the most, or whatever makes the most sense to you.
Some decisions require more consideration, though they are not life-changing critical decisions. You might want some guidance. For these ask God for guidance, then listen to the two witnesses inside yourself for an answer. If one choice makes more sense to you, or if one feels more emotionally correct, you may have your answer. Don't be hasty: Take the time to make sure you've really thought everything through and you've considered all your feelings. When your heart says one thing and your mind another, take more time until you have harmony between the two, and the word is established on what you should do. Minor decisions probably don't require perfect harmony between mind and heart, but they should not be completely at odds either.
Major, or critical life-changing decisions obviously require the most consideration. You might be deciding who to marry, or what your career should be. In my case, many of my hopes, dreams, and ambitions were gradually lost after my wife took ill, battled cancer, and lost the battle. With the loss of so many hopes and dreams, I am redefining myself, and forming new hopes and dreams that I can still realize. I don't want to spend my life in front of a computer, so I'm reconsidering my career ambitions. I have a lot of these major decisions ahead of me, but not necessarily any more than anyone else. Before you make major life-changing decisions, make sure you have a strong balance between the two witnesses inside you. You should feel right about it emotionally, and you should be at peace with it in your mind. If you find a strong emotional pull, take time away long enough to hear the logical side. Let me give one example from the life of George Osmond. He felt a strong emotional tie to Olive. He told her he needed to move away, and left for a few weeks. She thought it was over because he didn't say he would return. He came back in three weeks because he knew he could not live without her, and told her as much. This time away probably gave him time to think logically and balance his heart and mind. They married and had nine children: Virl, Tom, Alan, Wayne, Merrill, Jay, Donny, Marie, and Jimmy. Major life decisions are naturally more emotional, so the heart-witness inside us often gives us strong emotions. Take time, and probably lots of time, to balance that strong emotional pull with logos. Make critical life decisions after both the witnesses inside you strongly agree.
For this discussion, I presented three types of decisions and how to make them based on how critical they are. Really, there are no clear boundaries. Some decisions are more trivial than others. Some decisions are more critical. Just remember this important guideline most of all: The more critical a decision is, the more you should pray and seek a harmony between the two witnesses inside you - your heart, and your mind, your feelings or emotions and your logic. In the mouth of those witnesses, you establish the path you should follow.
Members of my own faith might consider reading Doctrine and Covenants sections six to nine for more on how to listen with your heart and mind. I may add some references for other religions sometime as well.