Here are some examples:
* Cars are a major mode of transportation.
* Trees provide oxygen and shade.
* Music can evoke strong emotions.
* Love is a powerful force.
* The dog barked loudly at the mailman.
The key thing to remember is that a common noun is a general name for a person, place, or thing (e.g., car, tree, music, love, dog). It's not a specific name like a proper noun (e.g., John, Paris, Beethoven).
So, feel free to start your sentences with common nouns!