Gardens were originally intended to be used for growing food, however the modern day garden can be used to grow food or for strictly for aesthetic, pleasing reasons. Good garden designing is a combination of being prepared, figuring out your gardens purpose, planning the details and, naturally, planting everything.
Many believe that preparation is the core of good garden designing; before you start any physical work be sure that you carefully check out the area in both sunlight and shade. Find out where the ground is dry and muddy; see if there are areas that may end up having a water runoff problem. Draw sketches of what is currently in the area you want to use on graph paper, making sure you keep it to scale and then you are ready to design a garden.
Garden designing, when done correctly, actually reflects that particular gardens purpose; for instance, if you will be using the garden area for entertaining then you want to be sure to have seating areas and level walking surfaces. If you are going to design a garden for cut flowers then it is best viewed from a distance so that the flowers that have been cut will not be as visible as they would if the garden was closer to the house or patio. If the garden is going to be used for growing food then you need to be sure that there is plenty of room between the plants so that you will not pack down the soil when harvesting them.
You must also take things like water, soil and sunlight into consideration as they are a crucial part of your garden designing success because no matter how gorgeous the design may be if the plants do not live and thrive then the garden is basically a failure. You need to plan ahead of time what plants will go where; there are some plants that can grow equally well in shade or sun but most of them prefer one over the other so you should plan accordingly. The water factor is important as well when you design a garden as plants like roses like having the soil moist but do not like having water logged roots while trees prefer a good watering every couple of weeks. The same idea is true for the soil; some like sandy soil and others like rich moist soil so you should plan to group your plants accordingly.