There's a magic box to help you with list outlining. It's the List Outline Generator (LOG). You think of any generic theme such as Prayer, the Holy Spirit, Heaven, Love, or whatever. Now cast your eyes over the LOG. Certain words will suggest themselves as a specific theme to turn your generic theme into a list outline.
Let's say you have the general theme "sin" in your mind, and casting your eye over the L.O.G., the word "fruits" might jump out at you, and you'll think "The Bitter Fruits of Sin" would make a good sermon. Or the word "surprises" might suggest itself as "Surprises in Store for the Sinner". Or possibly "remedies" as in "God's Remedies for Sin" eg the blood of Christ, the seal of the Spirit, the penitent prayer.
This box doesn't work for everybody. Some like it, and for others it does nothing. If you've tried it and don't like it, that's OK. The lesson on list outlining works perfectly well by itself. The magic box is only for those who find the magic in it.