You can get a moisture meter that will tell you when the soil is dry. Palms generally don’t like to be water-logged.

I have a relatively new parlor palm. I had just been watered when I bought it and the salesperson said it wouldn't need water immediately. How much do I water it? Websites tell me how often or when to do it, but how do I know how much? I have never had to water something this big and I'm afraid of overdoing it. I just take a guess with my spider plants, but they are small and I know if I've gone over b/c it will come out the bottom. That would be A LOT of water for this palm.

My not-green thumbs thank you.