First, make sure that you have the right star chart. Choose a chart that shows your current month or the season. If you have a planisphere (a star chart with a disc that can be turned), make sure to turn the chart so the current month is showing. Next, turn the star chart until it faces the direction you are facing. For instance, if you're looking to the south, turn the sky chart so south is at the bottom.
A final orientation shift may be necessary since the time of the night also matters. Star charts indicate the representative time, so if you are not at the given time, you need to rotate the chart slightly to match what you see above. With the chart oriented, you can now match it with the night sky. Look for star patterns and star sizes.
Most star charts indicate the brightness of stars by the size of the circles. Brighter stars are indicated with bigger circles than the dimmer ones. Look at patterns of bright stars in the sky, and try to match them with the patterns of big circles on the star chart. For instance, in the northern hemisphere, identifying Orion is a great place to begin, since not only does are there three bright stars lined up making Orion's belt, but there are also two bright stars in Orion. Another good constellation is Cassiopeia, which has five bright stars forming a "W."