I used to say Livebearer males wear a Sword (gonopodium) thin and pointed
and females wear a Fan (wide single fin under belly)
Cichlids there are so many species it will depend on which one.
But as a general rule, males tend to have longer more pointed fins and MAY be more colorful or different color. They also may have a nuchal hump on their heads.
Google is your friend. Look at pics of male and females and you'll quickly get an idea.
Some fish are more subtle. Livebearers are easy !