What if one of your team members appears to be a problem? He or she may not fit into the team and having such a person among the others may prove to be too risky. People are getting infected with examples of bad behavior way too fast. (I wish they did as well mimicking something good, *sigh*)
The first advice is not to lay it off for too long. Yes. This is harsh business but it has to be done. Otherwise what kind of a manager you are? I usually start fro, talking to a person explaining him or her: what is wrong with the behavior and how it affects the team. Once a person is aware of the problem he or she can do something about it. In this respect, this is a service to a person that you do.
It may not be as easy though. Some people take critics personally. It may make your efforts all in vain. It helps to explain that the reason you are talking to your team mate now is not to "put in place" but to help, help to grow, help to get better.
Mostly, things are looking too good from the inside. We all fool ourselves that we work as well as it can only be. The reality is a little bit different. The extent in which it differs depends on our inner qualities. Some assess their achievements with due criticism. Some think that they do much better than others having no real reason to think so.
Your goal is to provide objective feedback on the achievements. Do not forget to mention good ones. It will make your team mate more open to discussion. And it's always better to start meeting from talking about positive achievements. Remember, you goal is a constructive discussion. Having someone in bad resistive mood will make things much more complicated.
Once you delivered your viewpoint explain the consequences. I usually make it clear if I am going to let a person go in case there is no progress on the improvement plan. This is tough but fair. Do not try to make corners flat. Just put it clear.
Then sit together and define strategy of how to make it all better for a person and for the team. Once you have a plan, define deadlines and metrics that will help making sure you have achieved the goals.
Following these simple recommendations may save you a lot of time and nerves.