When To Water, How Often, And How Much Is Enough
We think you get the point
Well, congratulations! You are the proud owner of a highly complex and sensitive water tester: Your finger. While there are exceptions (read any tags/packages that came with your plants/seeds), most plants should be allowed to moderately dry out between waterings. The potting mixture should be lighter in weight and color, and should feel dry and crumbly. If your plant starts to wilt, you've waited too long.
At this point, water "deeply." By this we mean, if you're top watering, pour enough into the pot that a little runs out the bottom. You should have drainage holes and catch basins so that this won't make a mess. See "Watering Methods" for more details on - you guessed it! - different watering methods for your plants.