The Proclamation Trust have a free booklet by Sinclair Ferguson called Preaching Christ from the Old Testament.
Here is the bio:
“Preaching Christ is the great purpose of the Christian expositor. But how do we preach Christ from the Old Testament without falsely allegorizing or spiritualising? Sinclair Ferguson shares some principles that will help us to stay true to the original purposes and historical reality of the text, while drawing out the riches of grace which are proclaimed in Jesus Christ
While the temptation is to look for a simple formula, a quick fix, which will allow us to do this without effort, Sinclair Ferguson wants to help us become preachers with an instinct for preaching Christ from the whole of scripture.”