"Most of your initial thoughts are not worthy of the light of day," the former first lady told a summit of young leaders hosted by the Obama Foundation.
Ms Obama's comments drew laughter from the audience as she added she wasn't "talking about anybody in particular."
The US President is known for his frequent use of Twitter, and even credited it with helping deliver his election win.
"Without the tweets, I wouldn't be here," Mr Trump previously told the Financial Times.
Ms Obama described the platform as a "powerful weapon.
She said when people tweet, they need to think it over, spell correctly and use good grammar.
Ms Obama went on to say going on to say "every word you utter has consequences. Words matter at this level."
She added: “You’re careful with your words. You’re careful with how you debate.
"And I think when you’re the first lady or the president, the commander in chief, and you have that voice, and that power, and that platform, I think what comes with that is the responsibility to know that every word you utter has consequences.”
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