A bromide is a common saying or proverb that is obvious and not that helpful, like "When life hands you lemons, make lemonade."
Some people love to say things like "Follow your dreams" and "Love takes hard work." Such trite, clichéd sayings are bromides. A bromide isn't very helpful or specific, and people tend to say them over and over again. The word bromide comes from the chemical compound made of the element bromine and another metal. This kind of bromide was historically used as a sedative, a medicine that dulls your senses, just as figurative bromides are boring and dull.