1. Gospel preachers are not the only ones preaching, 1 Cor 1:20).
2. In Christian preaching, substance is far more important than style,1 Cor 1:17f.
3. Preachers should be wary of gaining a response by mere human eloquence; far less by emotional manipulation., 1 Cor 2:4.
4. No preacher worth their gospel-salt will shy away from preaching the ‘crude’ subject of the crucified Christ, 1 Cor 1:23).
5. Unbelievers will demand other things from the preacher instead of the gospel, 1 Cor 1:22f.
6. Eternal destinies hang in the balance every time we preach. 1 Cor 1:18.
7. The gospel is powerful to save all who believe it, 1 Cor 1:18.
8. The gospel message is not limited to the people we think are most competent to receive it., 1 Cor 1: 26.
9. Preaching that changes lives relies on the powerful working of the Spirit, 1 Cor  2: 4f.

Based on this article by Colin Adams.