#1: One-on-ones
Spend some quality time with them. Giving them a chance to talk out their thoughts allows you to see issues before they get too big -- and in many instances allows you to cut off potential problems before they manifest themselves.
#2: Coaching
Take the time to ensure that they know what they should be doing on their project, or maybe when their next deadline is. Providing positive feedback when things go well and constructive criticism when tasks go wrong is all part of the process.
#3: Paying attention
When asking questions, try to put yourself in your team members' shoes. There could be something going on in the office you are not aware of. Or maybe something is happening in their personal life that is spilling over into their job.
#4: New projects
Resolving some issues is as simple as giving employees a more challenging project. A work environment devoid of challenges (and their associated successes upon completion) can easily lead to boredom, which can turn a happy employee into an unhappy one.
#5: Training
Sending one or more employees to a class to work on a new skill or learn a new technique -- or even just allowing them to attend a seminar -- is a great way to jump-start people. Having something new to learn and bring back to share with others can motivate not just individual members but the entire team.
#6: Money (not)
Very rarely does money solve the problem of an unhappy employee. In some instances, money problems might be a contributing factor in their unhappiness, but overall, that won't be a root cause.
#7: Time off
Employees all like to have a few days off now and then that aren't part of their standard compensation. Just make sure it doesn't turn into an expectation for them or anybody else on the team or it could turn into a bigger problem for you.
#8: Telecommuting (WFH)
There is nothing worse than commuting back and forth to work each day. With the length of the typical daily commute now more than 30 minutes, employees are increasingly frustrated with the long lines of traffic and the cost of fuel. Allowing employees to work at home one or two days a week can help with this problem. And you get the added benefit of keeping another car off the road!
#9: Mentors
If you can find somebody employees trust and respect, someone who will inspire and challenge them, the potential for their growth and happiness can be endless.
#10: Moving on
Sometimes no matter what you try, things are not getting better. In these situations, the best thing you can do is to help the employee find a different situation -- either elsewhere within your organization or in extreme cases, outside it.
BONUS
Keep it positive
Being a true leader means getting the most out of your team no matter what the situation. One of the best ways to do this is by keeping in touch with your team while providing constant feedback. Positive feedback when things go well is as important -- if not more important -- than negative feedback when issues arise. Most of us know when we make a mistake. We usually just need somebody to pick us up, dust us off, and point us back in the right direction.