The big thing you need to know is that if you over-water you plants, you will most likely kill them. You also have to remember that even though the soil looks dry on the TOP, there may still be plenty of soil underneath the surface that you cannot see. You will eventually learn the signs of exactly when to water. What I typically will do is wait for the plant to start wilting just a tiny bit. (It will start to droop a little, and the leaves will start to curl.) Once you see that, go ahead and water the soil like AJ said...get the soil MOIST, but not soaking wet.
A good way for a "beginner" to learn the correct watering processes is to put your plants in a clear container. (Clear CUP.) Hope that helps!