Here are some good posts on preaching:
How Long Should A Sermon Be – Brian Biedebach (Preachers & Preaching)
The message must last long enough for the text to be rightly explained and the practical implications properly developed….
Why Sermons Often Bore – Gavin Ortlund (TGC)
…how to preach to the heart, and through the heart to the whole person.
Top 500 Preaching Resources – David Murray
A treasure trove of opportunities to grow in our preaching!