You can recognize law preaching because it’s always full of references to the Bible being a “handbook for life,” full of principles for a successful life. If your Bible is just a handbook for life, throw it away.
The Bible is the story that delivers us the Gospel. It’s point is to get you to Jesus, the one mediator between God and man. It’s a big book to get you to a short message. You buy the whole field, but the treasure is the Gospel, not the book of Judges or financial principles from Proverbs. Once you have the Gospel right and you know what preaching is all about, then you can read and preach Leviticus or Malachi or whatever you want, as long as Jesus is in his proper place and the message is the Gospel, not the law, or the old covenant, or this week’s good advice.
The Law vs. The Gospel
Check out this post about the law against the gospel or legalism against mercy.