If you plan on adding water lilies to your pond, the location you choose should receive a minimum of 6 hours of sunlight a day.
Ensure that there is easy access to water and electricity.
Choose the most level site available while avoiding low level areas where rain could carry in pesticides, herbicides and possibly flood the pond.
Also, try to avoid positioning the pond where it could catch falling leaves. Leaves will sink to the bottom, decompose and release toxins which may be harmful to fish and plants.
Try to avoid placing the pond in areas where the soil is prone to saturation. This can cause the liner to possibly float.
Try to place the pond in an area where it can be visible from the house where you spend most of your leisure time; either from the kitchen window or the deck, as an example.
Before digging, please consult your local building ordinance for codes and check for any under ground utility lines.
Also, it would be a good idea to make an electrician aware of your water gardening project and have him or her install ground fault interrupter outlets to ensure that the equipment runs safely.