This is a very good question and I think you pinpoint a real issue in how we understand God speaking to us.
The Bible teaches that God speaks through Jesus (see Hebrews 1:2) and the way that we hear Jesus is through the Scriptures - the Bible. The Scriptures are described as breathed out by God (2 Tim 3:16) and as the Word of God (Mark 7:13). This is very important for us. It means that while God can speak to us however he likes, he has promised to speak to all of us through the bible. So if you want to hear God, read, study and discuss the bible (especially with others). This helps us in two important ways:
Firstly, anything we think or believe about God must be measured against the Bible. If what we think God is saying to us goes against what the bible says, then it is not God talking to us. This is how we recognise Satan’s temptations - they will not be in line with the Bible.
Secondly, it means that we won’t waste time searching for God’s voice outside the Bible. If you want to hear your favourite band you check the tour dates and you go to the correct venue on the correct night. You don’t say - well they might play at this particular club tonight so I will go there. No, you go by the published tour dates. It is similar with God - he has promised to speak to us in the Bible and he has told us that the Bible is ‘living and active’ (Hebrews 4:12) - it is not a boring old document - it’s God’s living and active word.
So, the answer to your question is that I know that God is speaking to me when I read the Bible. So the most important thing you can do when you read the bible is to ask God to speak to you through it.
I hope that helps - please come back to me if you have other questions.