Therefore, to one who knows the right thing to do and does not do it, to him it is sin. (James 4:17)
Making good decisions is making godly decisions. The etymology (word origin) of the word "good" is "God". So making good decisions is really about making godly decisions. When the rich young ruler addressed Jesus as "good teacher", He responded; "Why do you call Me good? No one is good except God alone." Jesus was saying that He was not only good, He was God!
To make good decisions, we must make godly decisions... Decisions that are pleasing to and will bring glory to God; Whether, then, you eat or drink or whatever you do, do all to the glory of God. (1 Corinthians 10:31) It is also of course true that one who knows the right thing to do and does not do it, to him it is sin.
So how do I know the right thing to do so that I will make godly decisions? If you are a Christian, you already know the answer to that question. God's word, the Bible, gives us His will. We are to be imitators of God, as beloved children. (Ephesians 5:1) As we are saturated in God's word, our lives become conformed more and more to that of our Lord Jesus Christ. We know His will and, therefore, we know the right thing to do and are equipped to make good or godly decisions.
Knowing God's will not only equips us to make the right or godly decisions, but also constrains us from making the wrong or sinful decisions. Paraphrasing something Dr. John MacArthur once said; "The problem with being so well acquainted with and having memorized much of the Bible is that whenever I am tempted to sin, a hundred convicting Scripture verses pop into my mind!" Thankfully, God's word can be very convicting, as well as instructive!
Most decisions are obvious, but what do you do when the Bible doesn't seem to give you clear direction? What do you do when you need more wisdom? The answer is to ask God; But if any of you lacks wisdom, let him ask God, who gives to all generously and without reproach, and it will be given to him. (James 1:5) When one of God's children comes to Him in prayer seeking His wisdom, he or she can expect Him to answer. He will answer generously and without reproach (i.e., without reprimanding, rebuking, criticizing or condemning our ignorance). Just like we hope we would answer whenever our children come to us for wisdom and advice about a difficult decision.
To make good decisions that are pleasing to God, look into His perfect word and prayerfully seek His perfect wisdom. Maranatha!