Your laboratory is not a factory. The people in your lab are smart, creative, self-motivated technical professionals. If you want them to do their best work, and your lab to work at peak efficiency, you need to manage people effectively and appropriately. Here are a few pointers.
1. Measure outcomes, not inputs.
It's not how many hours people spend in your lab that matters; it's what they accomplish while they're there. You don't want people taking up space, spinning their wheels for hours on end and not accomplishing much. A good part of the difference between a very good advanced student and an accomplished principal investigator is efficiency: Successful PIs, especially those who participate fully in raising their children, have learned how to get the most done in the least possible time. Good people will get the work done, even if they have to go home at five to cook dinner for their children. If they aren't enjoying their work and their lives, you--their boss--aren't getting the best they have to offer. So let them have lives and try to keep them happy. If they're in the lab because they want to be, because there's work they're eager to get done, they'll be more productive.
2. Don't measure outcomes overzealously.
Some problems are harder--and take longer to solve--than others. Just because one of your trainees is getting results right now and another isn't doesn't mean that the first is working harder, or better, than the second one. The postdoc who doesn't seem productive now may very well be the one who makes your lab's next big breakthrough. If you try too hard to measure performance and screw it up--an easy mistake to make--it could blow up in your face.
3. Keep your commitments
Whenever you make a commitment to someone in your lab, write it down and keep it. It may not be important to you, but it could be very important to them. If you tell a postdoc that she or he can be first author on a paper, make sure it happens.
4. Treat people decently.
It's never OK to abuse a subordinate, verbally or otherwise, but even if it was OK it would still be a bad idea. You'll get far better work--and more of it--from a happy postdoc than from one who feels stuck in a lousy job with no future and an abusive boss. It also makes sense to pay as well as you can, because decently paid people are demonstrably more productive than people who work for peanuts. It's not really about the money--most scientists throw their heart and soul into their work because they want to--but you have to make it easy for them to make a commitment.
Keep in mind that you are likely to have people in your lab who are very different from you, who don't think like you do, and who don't (necessarily) share your values. In these cases, your basic human decency may not serve you well; you may need to work at achieving and maintaining a comfortable working relationship. The key is good form.
5. Remain approachable and listen.
Postdocs tend to be self-motivated professionals, and they generally can be left to their own devices. Graduate students typically require more guidance, but some of them are at their best when they're left alone. Even the best students and postdocs, though, will need your help from time to time. There are other places they can go for help, but it's your lab. So make yourself available. Do your best to ensure that your people feel free to turn to you with any questions or concerns.
But this makes it sound too one-sided. You are also likely to benefit directly from enhanced two-way communication. The people in your lab can inspire you by asking--and occasionally answering--questions that hadn't occurred to you.
6. Establish reasonable policies, communicate them clearly, and stick to them.
Disputes over authorship and project ownership arise in every laboratory, but if everyone knows the rules ahead of time, and if those rules are enforced consistently, these disputes are much more easily dealt with. It's impossible to anticipate every possible conflict, but a set of simple and rational guidelines will go a long way toward diffusing--and avoiding--conflicts.
7. Keep some slack in the daily schedule.
An organization that is working at full capacity lacks time for reflection and resources with which to adapt to change. Both are essential for the success of a discovery-based enterprise. Sometimes it's not a good idea to push too hard.