Determine the approximate flow rate you want and the approximate total length of your pipe. Consult a friction loss chart to choose the proper diameter pipe. Choose a pipe diameter that keeps your friction loss below about 6 feet per 100 feet of pipe. The longer your run of pipe, the more critical it is to minimize your friction loss. Use a filtration system that does not require a lot of pressure.
Biological filters work well and require very little pressure.
It is extremely important to make sure the water supplied to the pump is FREE of debris. Never allow a horizontal centrifugal pump and motor unit to become submerged. If this ever accidentally occurs, shut the unit down, disconnect it, and have a reputable service shop examine the motor before using it. Never run a pump dry. This will damage the seal and impeller.