Whether you are in charge at work and trying to make sure everything gets done both well and on time or just an employee trying to optimize your own performance in hopes of getting a promotion, you need to keep in mind that longer hours are not always the best way to improve productivity. There comes a point past which more hours can actually lower productivity by increasing sloppy work, slowing people down due to fatigue or even causing accidents on the job.
Know when to quit
If you want to put in some extra hours to try to enhance your career, know when to quit. Know when pushing for more is simply counterproductive. Find a way to track your productivity to see if more hours is really getting more work done or if you are just taking longer to do the same amount. Watch for signs that you are simply too tired and can no longer work effectively. If you are the boss, consider the possibility that sending people home at regular close of business so they are fresh the next day may be one of the best things you do on a regular basis to enhance long term productivity.
Sharpen the axe
Probably everyone knows the story of the two guys who cut wood all day and the one who took breaks regularly got more done because he sharpened his axe every time he sat down. If you find you or your employees are just not getting enough done, consider improving training or providing better tools instead of simply putting in more hours. Perhaps the process is not optimal and there is room for improvement.
Keep an eye on health and wellness
For individual employees, the usual advice applies: try to get enough sleep, eat right and exercise. Someone healthy and well-rested will get more done in the same hours than someone short of sleep and not under the weather. If you are a manager, consider starting a wellness program or other program to encourage employees to eat right, exercise and generally take care of themselves so they can bring their A game to work more consistently.
All things in moderation
You just really need to remember to not get so focused on raising productivity that you kill productivity in the process. People who are overworked, not eating right and not getting enough sleep are simply not going to be at their best. People are the most critical asset at work. Do not lose sight of that fact and run them into the ground.