A yellow edge means that it's not getting enough water, while a brown edge
means it's being overwatered. But, I've had a corn plant where the edges
are both colors. For watering, I bought a soil tester (its a metal stick
with an indicator at the end) which tells you when the soil is dry(3),
moist(somewhere from 4-6), and wet( over 6). This costed like 10 dollars.
For the corn plant, in winter, it only needs to be
watered when it's around 3 or four. The important thing is not to let the
roots dry out. In summer, you can water once a week, and basically keep
it moist. For the ficus, I water very infrequently, maybe like every two
weeks, but for this plant I'm not sure. Good luck with the corn plant!
(also make sure its in good sun)