When people think they are making a difference, they are very likely to work harder so that the desired results are realized.
There is a school of thought that feels only positive forms of motivation ought to be utilized in the workplace, making discipline a sensitive subject at times. Discipline is still vital at times, even if much more can be accomplished with positive reinforcement and motivation. This doesn't mean you should bully people but at the same time if an individual consistently makes the same mistake and you discover it's because of negligence, for example, then you have to discipline that person promptly and effectively. However, do not dwell on it and be sure to offer rewards when their performance meets or exceeds your expectations.
Motivation is a matter of being aware of what pushes the people on your team. The better you know the individuals you manage, the easier it will be for you to motivate them and ensure their performance meets or exceeds your standards. The above mentioned suggestions are a good point to start but remember that not everything will work. The secret to easy motivation is to really become familiar with the individuals on your team.