Focusing on the season:
* Autumn, with its vibrant hues...
* The crisp air of autumn...
* As autumn descends upon us...
* Autumn, a time of change...
* The golden days of autumn...
Focusing on the atmosphere:
* The smell of fallen leaves...
* The sound of crunching leaves...
* The cozy feeling of autumn...
* The warmth of autumn sunlight...
* The melancholy beauty of autumn...
Focusing on specific aspects:
* The harvest moon of autumn...
* The changing colors of autumn leaves...
* The first frost of autumn...
* The pumpkins and gourds of autumn...
* The scent of cinnamon and nutmeg...
More creative options:
* Autumn whispers secrets...
* Autumn paints the landscape...
* Autumn holds a bittersweet charm...
* Autumn is a time for reflection...
* In autumn, nature prepares for slumber...
Ultimately, the best way to start a sentence about autumn depends on what you want to convey!