As mentioned, individual plants will require different amounts of water to keep them growing optimally.  But what all plants do like is moist soil.  If you are worried about over-watering your plant, make sure that the pot you choose has a good drainage system.  With holes in the bottom of the pot or gravel inside the pot the soil and plant will soak up the necessary water and the excess will run out through the bottom.

If your houseplants are not thriving no matter what you do, there are two things to look into.  If you are using tap water to water your plants there may be too much chlorine or salt present.  A solution to this is to use distilled or filtered water or you can leave a container outside to collect rainwater.  Either option is acceptable and may be the change you need to make to grow healthier plants.

Choosing to fertilize your plants is another way to give them a boost.  Fertilizer contains nutrients and elements that plants need to grow.  Indoors plants do not need as much fertilizer as their outdoor counterparts do.  Because of a slower rate of growth, feed your plants minimal fertilizer.  In the winter time you can probably skip this step altogether.  The spring or summer time is the best time to fertilize indoor plants.  This is during their growing phase when they need the extra nutrients the most.

Taking a cutting from a plant is also known as propagation.   If you have a hardwood plant that you want to propagate the process is slow but easy to do as the cuttings are quite hardy.  Take the cutting (about 5 inches worth) when the tree is dormant (in the middle of winter) and place the cutting cut-side up in a pail of sand.  Fill the pail with water and wait until spring.  Then submersed side will have little nodules that will turn into roots once planted.

When you are taking a cutting from a soft-wood plant, it will require more care and attention.  Taking cuttings from soft-wood yields quicker results and you do the actually cutting when the plant is in the active growing phase.  You are cutting off the new growth back to a nodal (from the point it stopped growing the year previous).  This method
benefits from the use of a root producing medium found at nursery stores.  It is important to place the cutting (cut-side down) into the root medium immediately.  If the cutting dries out it will lessen the changes of a successful cutting.

Next, pick a pot or container suitable to the type of plant you are growing and plant it once the roots have developed.  At this point, you can follow the regular care instructions for the type of plant you have just propagated.