Well-maintained and beautiful hedges can provide privacy, act as a barrier to street noise not to mention add value to your home. Hedges are smaller shrubs, that when planted in rows, grow together to make a uniform wall or shape. Trimming your hedges shouldn't take more than an afternoon, depending on how long your shrubs are and how much you plan to cut. You will need either some electric shears (if it's just a slight trim) or some pruning shears (if you plan on cutting the shrubs back more than a foot). Also, an old sheet and a rake will aide in clean up.
If you are cutting some already established hedges, or just taking the small new growth off the top and sides, then use an electric shear for the job. It will easily allow for you to cover a large area and shape the hedge quickly. As with all power tools, make sure you have eye protection.
If you haven't been caring for your hedges regularly, and need to take more than a foot off, you can use a hand pruner to cut the large branches and thin the hedge. Using small hand cutters can take more time, but they can also give a more presentable, soft natural look. Electric trimmers can finish a job quickly and still provide the same look of a skilled gardener.
You want to decide beforehand how you are going to shape your hedges. Square and round shapes are usually the best options. What is your purpose in trimming? Height, width, thickness, all three even? Try to keep the shape natural, with not too much of a flat top if you live in an area that gets heavy snows. In the winter, the weight of the snow on small shrub branches can damage and break the support branches.
A rounded shape will allow for more sunlight to reach the leaves and encourage re-growth. When you trim before fall and winter, know that the hedges will take longer to grow back, as opposed to the rapid growth seasons of spring and summer. You should trim when there is less than a foot of branch that you want to trim. If it is anymore than a foot, wait until the spring to trim when the plant will be able to re-grow leaves and fill in spaces quickly. Hedges with smaller leaves (boxwoods) and deciduous hedges (elm and beech) will recover quickly from pruning mistakes, and are great for beginner practice.
With your plan in mind, start at one end and begin to trim back the hedge. If you are using an electric trimmer to just take off the tips of new growth and shape the plant, then use a sweeping motion over the tops and sides to slowly remove the growth. If you are using hand pruners and cutting more than a foot, reach into the hedge and start with the large branches to be trimmed first. This will slowly open up an area for you to work in. When one branch stems out into two, snip it just above the Y shaped split. Trim a few feet of the row, step back and look and make sure you are following your plan. If so, proceed on down the hedgerow.
After you are done trimming, use the rake to pull off the cut branches and sections from the top and sides of the hedges. Make a pile of all your hedge trimmings every few feet. Now you can either bag the hedge clippings, or rake them onto an old sheet and pull them to a clipping waste area if you have one. Now take a step back and enjoy your hard work!