Learn to discern the message on which God would like you to preach. For some, God may reveal His message the week before the sermon, for others the day before, and yet others even on the same morning as the sermon is to be preached. For me personally, God reveals His messages during the course of a few months, usually through my sufferings. In applying His messages to my own life, I would often experience miracles and testimonies which I can then include in my sermon. In this way, I can also re-assure myself that what I have heard from God is authentic because I have proved it to work.
A good sermon content should typically include both theory (information) and practice (testimonies). Sermons which include only theory could be perceived as lacking the element of "reality". The practical aspect of the sermon may not only cement the theory, but also helps to illustrate how that theory can be applied to everyday lives, to real life situations, and equally important - the results that it gives.
The average attention span for most adults is 45 minutes, so ensure that your sermon is not too long or you risk losing their interest. You do not want to be famous for doing long sermons as this will cause people to avoid going to your sermons. Ideally you want people to be excited about your sermons, so that not only would they turn up, but that they would actually be looking forward to listening to you.
Create an interesting title for your sermon, a title that arouses curiosity.