Michael Bird had an interesting post recently on the level at which you should preach. There's always the danger of going to one of two extremes when preaching – making it far too academic, or far too simple – both of which have the same result of not helping those who are listening to grow and mature in faith. Bird offers a few points for consideration:

What I try to do in my homiletic journeys is: (1) Identify with your audience. Preaching to a youth group ain't the same as speaking at a retirement village. But make sure everyone can grasp what you're talking about. When in doubt, simple is better. (2) The form should be easy and aesthetically nice to hear, but the content should be theologically informed. (3) Remember, preaching is based on good exegesis, but it is not a display of your exegesis. (3) Preaching is about persuasion, changing peoples' hearts and minds, not just imparting more information; and (4) The most important elements of the sermon are the first thing and the last thing you say, so find a way to make it sing and sting!