Well, "scientifically," you should stick your finger into the pot to check for dampness.
Indoors, the top of the soil may dry out a bit, but be really wet under an inch or so. It's easy to overwater in winter. Also, don't be too concerned if your croton drops a few leaves while indoors. Cut back on water if the leaf drop is severe. Don't know what part of the country you're in, but you may want to set the pot outside during the warmer months. It will be happier on the patio.