Outdoors in the summer, you may need to water them several times every week. Indoors they use less water. Water should be at room temperature. Crotons like it warm, but not hot. Hot and dry is especailly hard on crotons.
High humidity is essential for a healthy croton.
The plants should be misted regularly and kept on a humidty tray indoors. Let the plant rest during fall and winter. Use a quality, peat-based potting soil such as Bachman's Exceloam or Hyde Park Professional Potting Mix. Keeping in mind that crotons like to be somewhat crowded into their containers, repot them in late winter or early spring when needed. Their large leaves can collect dust which clogs the plants pores and interferes with the leaves collecting available light.