Question

what would be a good topic sentence for me if I were to write an essay on my favorite season being autumn

Answer 1

You could use something simple like: "In my essay, I will be talking about my favorite season..."
Or if you want to sound more creative: "The fall season is by far the best time of the year, because..."
Or you could begin by explaining what fall is like: "Fall is such a beautiful time of year because of all the colorful leaves..." or "Fall is so much fun because of Halloween..."

Answer 2

This is 3 sentences just to maybe give you an idea. Make adjustments as you please: Imagine a cool breeze brushing against your skin as the sun warms you to the perfect temperature. Imagine leaves of red, orange, and yellow blowing in the breeze. No need to imagine anymore because that's where autumn comes in.