Parallel structure in lists means combining like items in similar phrasing so there is not a portion of the list that sticks out or seems inappropriate compared to the others. If you must add an unusual item to a list, include it at the end to minimize the feeling of interruption.
INCORRECT: The woman ordered the painters to bring paint buckets, paint, paint rollers, a clipboard for them to write down her instructions and work clothes.
CORRECT: The woman ordered the painters to bring paint, paint buckets, work clothes, paint rollers and a clipboard for them to write down her instructions.
Parallel structure involves using list components from the same part of speech. Doing this enhances readability and adds fluency to your writing. While it is not a grammar ‘rule,’ employing parallel structure by using the same parts of speech or the same type of activity in each portion of the list improves your readers’ understanding of it. It is a part of the style.
INCORRECT: The painters put on gas masks, painted neatly, tried their best to not drip paint on the floor and talked quietly while working, but the customer was exasperated with them, nonetheless.
CORRECT: The painters wore gas masks, applied paint neatly, avoided dripping paint on the floor and talked quietly while working, but the customer was exasperated with them nonetheless.
Organize your thoughts before you write the sentence that is to contain a list. Keep lists together with the same types of items, similar activities or grammar phrases and diction, so the list elements have a sense of commonality. Also, if one item seems to stick out, then reword it or rewrite the sentence. Not every list reads well as a list.