Digging out the hole and laying the protective underlay and pond liner should, in most cases be relatively straight forward provided that you are not trying to tackle the job on your own!
The most difficult step to get right in pond construction is laying the edging. If it is done properly following careful planning, the result will be a pond transformed into a magnificent garden feature. 

Whether your plan is for a formal or an informal pond, the type of edging you choose is a matter of choice. The surrounding landscape generally influences this decision. The use of paving stones is popular for formal ponds whereas stones, pebbles and planted edges are popular for informal styles.
Wherever possible the choice of material should overhang the edge of your pond to protect the pond liner when the pond is of this type of construction (versus a preformed or concrete construction). When adding the edging make sure it is very stable and will carry the weight of being walked on without subsiding. 

Materials for pond edging

• Timber: provided that it is properly treated, timber can be used both to edge a pond and as the main structural material as in the case of a raised pond created from railway sleepers. A practical material which is best used for formal creations. 

• Stones, slabs and bricks: most effective for square, rectangular and circular ponds – of a formal style. Carefully planning needs to be done before pond is excavated to make sure this type of edging is going to fit exactly without having to compromise the design by cutting the last slab or brick to try to fit it in. The pond also needs to be constructed so that it is level from side-to-side and the land around it also level before the paving is laid. Remember to leave sufficient width of pond liner around the margins of the pond so that the paving stones can anchor down the liner. It is also a good idea to create a small overhang over the edge to protect the pond liner from UV rays as well as to disguise the point where the liner overlaps the surrounding soil. The image to the right shows a neatly installed pond liner with the overlap secured in place using boulders strategically placed around the pond. However, there is a rim of exposed pond liner, which risks being punctured by the claws or beaks of visiting wildlife).

• Plants: although not always regarded as a form of edging, but with the correct choice of mat-forming plants of tumbling growth, they can be most effective. Ideally plants should be evergreen varieties that prosper in moist soil conditions. Irises are a good example as they have tightly knot roots which will form an erosion-proof edge to the water feature. The image to the right shows an example of a small garden pond with plants interspersed with small rocks to add character to the edge of this precious garden oasis.

There are so many options available for the practicalities of securing the pond liner in place and to further enhance the most attractive feature of your garden. 

A final tip: when measuring-up your pond to order a pond liner, add an extra 0.2m to your calculation for the overlap of your liner so that it goes over the edge of your pond to which the edging material is placed to hold the pond liner in place.