The prerequisite--submit your will to the Lord.
Luke 22:42
John 5:30
John 6:38
John 7:17
Romans 12:1-2

The first place to look for God's will is in His Word.
Psalm 119:105,130
2 Timothy 3:16

God sometimes reveals His will through prophecy and revelations.
1 Kings 19:12
Ezekiel 3:10-11
Acts 10:19-20

God sometimes reveals His will through dreams.
Job 33:15-17
Genesis 15:12-16
Genesis 20:2-7
Genesis 31:22-24
Matthew 1:20-21

Seek godly counsel.
Proverbs 11:14
Proverbs 15:22
2 Corinthians 13:1

Consider obvious circumstances.
2 Samuel 5:22-25
1 Kings 17:1-9
Mark 14:12-16

Ask for confirming signs.
Genesis 24:14
1 Samuel 14:8-10