“Trust in the LORD with all thine heart; and lean not unto thine own understanding. In all thy ways acknowledge him, and he shall direct thy paths.” (Proverbs 3:5-6)
The key to knowing God’s will is willingness and determination to follow it before knowing it. “If any man will [literally ‘wills to’] do his will, he shall know” (John 7:17).
The best indicator as to whether one is really willing to follow God’s will, of course, is whether or not he is now following that part of His will which is already known, as revealed in His Word. This requires first knowing and believing, and then obeying the Word, especially those portions dealing with God’s general will for all Christians. “Thy word is a lamp unto my feet, and a light unto my path” (Psalm 119:105). Then, if one indeed is following the revealed will of God, he may ask in confidence (1 John 5:14-15) for the Lord to indicate His will in a specific matter on which there is no explicit biblical teaching (see also James 1:5-6).
God will then answer, though it may not be immediately. “Men ought always to pray, and not to faint” (Luke 18:1). It may not be in accordance with our preferences or personal judgment, but it will always be for the ultimate best. “For we know not what we should pray for as we ought: but the Spirit . . . maketh intercession for the saints according to the will of God. And we know that all things work together for good to them that love God” (Romans 8:26-28).
God will lead in two ways in the absence of specific Scripture guidance (which must always take precedence, of course). One is by providential circumstances, the other by inner witness of the Spirit, and these two must agree. Then, if all the terms have been met, one should proceed to follow God’s will as best he can, knowing that God will redirect him if he has made a mistake. God does want us to know His will, and He will “direct our paths.” HMM