These are probably some of the most quoted and instructive statements made on how to know God's will in the writings of Ellen White.
There are three ways in which the Lord reveals His will to us, to guide us, and to fit us to guide others. How may we know His voice from that of a stranger? How shall we distinguish it from the voice of a false shepherd? God reveals His will to us in His word, the Holy Scriptures. His voice is also revealed in His providential workings; and it will be recognized if we do not separate our souls from Him by walking in our own ways, doing according to our own wills, and following the promptings of an unsanctified heart, until the senses have become so confused that eternal things are not discerned, and the voice of Satan is so disguised that it is accepted as the voice of God. {5T 512.1}
Another way in which God's voice is heard is through the appeals of His Holy Spirit, making impressions upon the heart, which will be wrought out in the character. If you are in doubt upon any subject you must first consult the Scriptures. If you have truly begun the life of faith you have given yourself to the Lord to be wholly His, and He has taken you to mold and fashion according to His purpose, that you may be a vessel unto honor. You should have an earnest desire to be pliable in His hands and to follow whithersoever He may lead you. You are then trusting Him to work out His designs, while at the same time you are co-operating with Him by working out your own salvation with fear and trembling. You, my brother, will find difficulty here because you have not yet learned by experience to know the voice of the Good Shepherd, and this places you in doubt and peril. You ought to be able to distinguish His voice. {5T 512.2}