1. Always begin with data, with what we know for sure. Judge the unknown by the known, the uncertain by the certain. Adam and Eve neglected that principle in Eden and ignored God's clear command and warning for the devil's promised pig in a poke.
2. Let your heart educate your mind. Let your love of God educate your reason in discerning his will. The saints understand the Bible better than the theologians, because they understand its primary author, God, by loving him with their whole heart and their whole mind.
3. Have a soft heart but a hard head. We should be "wise as serpents and harmless as doves," sharp as a fox in thought but loyal as a dog in will and deed. Soft-heartedness does not excuse soft-headedness, and hard-headedness does not excuse hard-heartedness. In our hearts we should be "bleeding-heart liberals" and in our heads "stuck-in-the-mud conservatives."
4. All God's signs should line up, by a kind of trigonometry. There are at least seven such signs: (1) Scripture, (2) church teaching, (3) human reason (which God created), (4) the appropriate situation, or circumstances (which he controls by his providence), (5) conscience, our innate sense of right and wrong, (6) our individual personal bent or desire or instincts, and (7) prayer. Test your choice by holding it up before God's face. If one of these seven voices says no, don't do it. If none say no, do it.
5. Look for the fruits of the spirit, especially the first three: love, joy, and peace. If we are angry and anxious and worried, loveless and joyless and peaceless, we have no right to say we are sure of being securely in God's will.
Discernment itself should not be a stiff, brittle, anxious thing, but—since it too is part of God's will for our lives—loving and joyful and peace-filled, more like a game than a war, more like writing love letters than taking final exams.
Periodically, God calls us to do something that is very hard for us to do. He always supplies us with an ease of conscience and a sense of certainty once we start moving in faith.