When to trim
Knowing when to trim your hedges is the first step to making them look neat. New hedges require formative pruning for their first few years normally in winter or spring. After this you should move onto maintenance trimming once or twice a year depending on how formal you want it to look.
For small hedges a pair of hand held shears should be fine but for larger ones you will want an electric or petrol hedge trimmer. Regardless of what you use make sure it is sharp and lubricated. Always remember your safety equipment when using an electric or petrol trimmer. At the very least have safety goggles and sturdy gloves and remove all obstacles from the work space. Remember not to use power tools past shoulder height. If regularly trimmed the width of a hedge shouldn't really go past 2 ft. Remember that more formal hedges should be tapered on both sides so the base is wider than the top.
Cutting straight edges by eye can be very difficult so try using a taut horizontal string as a guideline and try using sticks or canes stuck into the ground for vertical lines. To shape the top of a hedge cut a template out of cardboard or plywood. Place the template on the hedge and cut along it moving it as needed. When using a hedge trimmer it works best to make a sweeping motion while keeping it parallel to the hedge for the best results.