Buy a moisture meter. They are only a few dollars and will save your plants. Water when the top 2+ inches is dry. You can poke your finger in there. But, some people worry you'll damage the roots that way. Or, if you're like me, you wont trust your finger! So, buy a moisture meter from any home and garden center.
When you water, let the water drain out the bottom -- not gush, just drain. Then, pick up your pot and remember how it feels. Pick up the pot again in a few days--notice the difference? Ok, now save all the trouble and go buy a moisture meter.