|Notice how the text and the image work together to make a point.|
So, I work from a stance of simplicity.
In many sermons I'll have one slide per major point. I do that so I can still move and flow within the sermon and have something visual to help connect my ideas for the people who learn best that way.
If you're just starting out take your three point sermon and turn it into a five slide deck.
Slide 1: Title Slide - this is the title of your sermon. This slide will be up while you introduce things, read scripture, etc. It should be mostly the title of your sermon and an enticing image that invites people into your text without giving away your point.
Slide 2: Point 1 - This should be a full-bleed image (it takes up the whole slide) with one or two words that define your first point.
Slide 3: Point 2
Slide 4: Point 3
Slide 5: Title Slide - Return to your title slide for your closing remarks (and so you don't have the black screen with "End of Slideshow" at the top). Ideally there should be a sort of ah-ha moment as the image you chose clicks for the audience.
You can find some good sources for images here.
You can find some good tutorials on using PowerPoint here.