Jesus once rebuked Martha for being busy with so much work instead of being like Mary who sat and listened to Him speak. Our Lord went on to say that what Mary did was the ONLY necessary thing in life (Lk.10:42).
We must all have the attitude that Samuel had, who said, "Speak Lord, your servant is listening". I want to listen to a man who listens to God - because such a man can teach me more in five minutes than theologians (with long 'tails' of degrees), can teach me in hours. John the Baptist could teach people more about God than Professor Gamaliel or any member of the Jewish Sanhedrin! When you listen to God, you won't preach what you've read in Christian books and magazines or heard from Christian tapes. The man who hears God speaks from revelation, not from academic knowledge or study. Such a man first experiences what he reads - and then speaks forth from his life. We must be especially careful to listen to God, when we have some important decision to make. God speaks to us through many ways.
God speaks to us primarily through His Word. If something is clearly written in God's Word, then we don't need to pray to find God's will, because it has already been revealed.
God also speaks to us through our circumstances. Our Lord has the key to every door (Rev.1:18) and when He opens a door no-one can shut it and when He shuts a door, no-one can open it (Rev.3:8). So our circumstances are very often an indication of whether God wants us to go along a particular way or not. We don't have to bang away at a door that God has not opened. We must of course pray, when we see a door shut. But if after repeated prayer, a door still remains shut, it may mean that God does not want us to go through that door. We must ask God to show us if this is so, or whether He wants us to continue in persistent prayer to open that door (Lk.11:5-9).
God also speaks to us through the advice of mature, godly brothers. Such men have gone through many experiences and they can warn us of pitfalls that we are unaware of, ourselves. We don't have to blindly obey them, but their godly counsel can help us.
God often speaks to us, while we are fellowshipping with other believers. Thus He teaches us our dependence on other members of the Body of Christ, even for revelation on His Word.
God always has something important to say to us, whenever we go through a trial or when we are sick.
God also warns us through the failures of others. If, for example, we hear of some servant of God who has fallen into sin, it is good to ask God what lessons we can learn from that man's failure (for we are all weak) and how we can preserve ourselves.
God can also speak to us when we hear news of evils being done somewhere or of accidents that have taken place. Jesus told the people of His time to repent, when they heard of Pilate butchering some Jews and when they heard of the accident in Siloam where a tower fell and killed some people - because such things could happen to anyone (Lk.13:1-4).
Let me add a word of warning however, against trying to hear what God is saying, by randomly opening the Bible and reading the first verse that you see! If you're eager to marry a particular girl, you may open the Bible at random to find some confirmatory verse. And if you don't find it, the chances are that you will keep opening the Bible until you find the verse that you want! That's how you can deceive yourself.
I heard a story of a man who was trying to find God's will in this way, who opened the Bible at random and read, "He went away and hanged himself" (Matt.27:5)! He opened the Bible again and found, "Go and do the same" (Lk.10:37)! He opened the Bible a third time and read, "What you do, do quickly" (Jn.13:27)! That cured him forever of trying to find the will of God in this way!
There may be times however, when we are under pressure, when the Lord may encourage us through a verse that we get, by opening the Bible at random. So this method is all right if you're looking for encouragement but not if you're looking for guidance. I want to encourage you to develop the habit of listening to God. This is the single most important habit that you can ever develop.