Understanding how to use 多 properly
Actually, 多(more) functions the same in both Cantonese and Mandarin  

Example:

"Eat fish more often "= "多吃鱼" (Mandarin) = "多食鱼" (Cantonese)

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The Cantonese term "多啲"(more) is equal to "多些"(more) in Mandarin. It can be placed before or after the verb. 

For example: 

(Mandarin)


多些吃鱼 = eat fish more often
吃多些鱼 = eat more fish


(Cantonese)


多啲食鱼 = eat fish more often
食多啲鱼 = eat more fish


(The real difference between Cantonese and Mandarin here are '食' vs.'吃' ; '多啲' vs. '多些')