There are many types of bamboo plants and several different methods of pruning.
Maintenance pruning for large running bamboo
Bamboo, like other plants, requires some pruning to maintain its attractiveness. Once each year you should remove older, unattractive culms and cut off any dead or unattractive branches. You can prune most bamboo without fear of damaging it. Just trim so it looks attractive. Make cuts just above a node, so as not to leave a stub that will die back and look unsightly. If you cut back the top, you may want to also shorten some of the side branches so the plant will look more balanced, not leaving long branches at the top.
Thinning Clumping Bamboo
Clumping Bamboo can be pruned to maintain upright growth, or thinned to maintain an airy appearance. If the plant gets too wide, just use a sharp pair of bypass hand pruners to cut some of the outer canes back to ground level. Start by cutting the most weepy canes at the outer base of the plant. Some of the taller canes that weep outward a little too far can be topped by cutting them just above a node, about 2-3 feet down from the top. This causes them to stand more upright.
For Screens or Hedges
As one might do with boxwood or other hedge plants, bamboo can also be pruned to form a hedge. This is best done after the new culms grow to full height in the spring or summer. Most of the new growth on a bamboo plant happens at the same time of the year, usually late spring or early summer for temperate bamboos. Do only one major pruning per year. If you want to control the size or height of your bamboo, and retain the natural look of the bamboo, this can be done by removing new shoots that are significantly larger in diameter than the culms that are the desired height. These shoots will be replaced by smaller diameter culms that will not grow so tall. This can be safely done with a plant that has been well established, not a newly planted bamboo.
Bamboo may be trimmed in topiary fashion. You may top the culms, remove some lower branches, and shorten some side branches and remove others. Any culms or branches cut do not grow back longer but only grow more leaves.
For display of colorful bamboos that have colorful culms you can enhance the beauty by removing smaller culms and cutting off lower branches so that the beauty of the culms is visible.
For dwarf bamboo it's best to cut the plants back to ground level every year, as you would with many ornamnetal grasses. This helps to rejuvenate the plant and keep it looking more full and bushy. Dwarf bamboos are also often trimmed later in the season to keep them shorter and more uniform in height. In very cold climates such as zones 4 or 5 dwarf bamboos may have their tops freeze back in the winter and still be good for landscaping. Just mow them as you should do in places where they don’t freeze back.