Welcome to the forum! You learn to write and become comfortable with writing by writing. From your introductory comment you seem to have good control over the mechanics of writing, so I anticipate you will not have significant issues.
I always suggest that folks write up a basic piece about 'why I would make a good shopper' because that narrative shows up so frequently on applications and a basic piece of a good or bad retail or dining experience. Be factual, avoid opinions and superlatives. Be descriptive (six black birds sitting on the telephone wire) rather than vague (birds sitting on the wire). Read your sample narratives aloud to see if they 'sound' right and perhaps have someone else read your samples. Then when you see a narrative requirement you will have that saved version to copy/paste into your application.