Most beginners to growing plants are warned not to overwater their plants. There are two common ways to overwater: using too much water at one time and watering too often. The best prevention is to find out how moist or dry your particular plant should stay so that you know when it's time to water. I have specific instructions for many plants, on this blog, and also feel free to ask about yours in 'comments'.
I was at a friend's house today and was asked why some of the plants were showing several yellow leaves. The plants were in their original growers pots and set inside of decorative containers. As I looked down into the containers, I could see that they were all sitting in water. We removed the plants from their decorative containers and dumped out the excess water. We talked about the the best way to water her plants. The last time I checked in with her, the plants had begun thriving again.
That is one way to overwater plants; pouring so much water into the pots that they can't use it all. It is wise to figure out how much water your plant will take so that only a small amount comes out of the bottom of the pot that will be absorbed quite quickly. If an hour or so after watering your plants, you see that there is water in the saucer underneath them, dump it out.
Watering your plants too often is the other way that they can be overwatered. Find out how much your plant should dry out before being watered. There are instructions for many plants, on this blog. Generally, the larger the pot your plant is in, the less often it will need water. My largest plants are only watered about once a month. Small plants in a windowsill may need water twice a week or more.
It's always wise to determine how dry the soil is by feeling it or using a soil moisture meter, before watering.