The more you know God the more you are able to distinguish his voice. When God speaks it will always be backed up by the bible as this is also His word. Knowing what is God and what is just conscious involves testing (1 Thessalonians 5:19-22), the following helps - is it biblical? Speaking to a mature Christian, listening to see if God says it again, then doing it – if it’s not immoral or unbiblical then God can use it.
The devil is a liar and deceives, he will always twist and contradict what God has already spoken in the bible.
HOW CAN YOU TELL THE DIFFERENCE BETWEEN GOD'S VOICE, THE VOICE IN YOUR HEAD AND THE DEVIL'S VOICE?