St Ignatius of Loyola, Father General of the Jesuit order, prepared a guide to help Christians distinguish the voice of God in their hearts and minds from other voices during prayer. Those others are one’s own voice (reason and imagination), the voice of the world (learned expectations and concerns), and the demonic voices which seek to confuse, isolate, embitter, and discourage. St Ignatius insightfully recognized that evil spirits attack a person differently in moments of weakness than in moments of strength. A summary of his rules can be found here. 

To that timeless advice, allow me to add a few further thoughts. 

Make a list of God’s qualities to remind yourself what He would or would not say, as informed by the history of holy exemplars, to compare with the things you hear.
— God is Love. 
— God always builds you up. He corrects but does not abuse or reject. 
— God’s words are typically gentle and beautiful. He is slow to anger, rich in kindness. 
— God calls us to communion with others, especially with family. 
— God calls us to perfection, but mercifully and joyfully embraces the most broken and wayward. 
— God often speaks through sacred scripture. 
— God lives through the Church and does not put us at odds with received wisdom. 

Remind yourself every day, if you have faith, that you were chosen by God. You are precious and protected. You will not fail. 

Remind yourself that many on earth pray for you. The communion of saints in Heaven are praying for you. Your guardian angel prays for you. You will not fail. 

The Lord is not an uninterested observer or impartial judge. He loves you more than anyone ever loved you. He pursues your heart with eagerness and knowing confidence. His providence is set in your favor. You will not fail. 

If ever you falter in faith, merely pray throughout your days. By both consolation and desolation, the Lord trains us to rely on His wondrous goodness and power. You will not fail.